It won't be needed, even if 'significant forces' are made available, there is no indication that communications and supply would enable them to attack and do much against 2nd Army guarding the flank of AG-Center.
Assuming the Southwestern Front re-establishes it's defences on the Psel river line, the 2nd Army would be strung out around 300 kilometers, roughly . Assuming the Soviets deploy even a quarter of the armies they had in the south against them and half of those they used in the OTL December offensive, they'll be facing nearly 8 armies when the Soviets attack. As to supplies, there would be multiple railheads running north from out of Kharkov, where the biggest depots for Soviet forces facing AGS prior to October were, and the Southwestern Front would still dispose of the bulk of it's plus whatever reinforcements it receives from the STAVKA. Furthermore, the lack of need to evacuate or destroy the industrial regions in the south with AGS stalling out so far to the west means there is a lack of need to evacuate them, allowing significant industrial output during the course of the autumn (instead of the pretty much collapse which occurred OTL), giving Soviet forces down there a relative wealth of munitions, weapons, and vehicles. The lack of needing to evacuate also frees up a lot of rolling stock.
Got some numbers of what was expended in August-September, what was stockpiled for October, and what estimated supplies on hand would be for September if they attacked east without moving on Kiev or Leningrad? Otherwise your fuel assertion really is nothing more than opinion. If the rains, which BTW impacted Guderian in his push south, but didn't stop him, do pause operations, it would be during the pocket battles, which were IOTL already impacted by heavy rains in the Vyzama-Bryansk area, but the Germans were able to advance anyway. I haven't seen evidence that the September rains were worse than the October ones, in fact considerably less bad, even if disruptive. But that won't stop the pocket battles, which will then prevent Soviet offensive actions in September and still result in the destruction of Soviet forces along the Moscow axis. Where are their replacements coming from? Soviet troops raised in September-December were not really combat effective, as OTL demonstrated, and mostly not assembled in front of Moscow; the later ones were east of Moscow, but the rest were around Leningrad or in the South. But again they weren't particularly useful for offensive action and fell apart on the defense. The units that held IOTL along the Moscow axis in October were pre-war formations finally arriving from the East, as they had been massively delayed due to loss of rolling stock and it's use evacuating industry. So if the Soviets do commit the nearly combat incapable reserve armies in any numbers in front of Moscow in September, they'd be more grist for the mill given their lack of nearly any heavy equipment and communications gear.
There were innumerable reports of fuel shortages in late-August. For example, on August 20th, XXIV Panzer Corps informed Guderian that it was unable to capture Novzybkov for lack of fuel. When pressed, the corps reported that 3rd panzer division was almost out completely, 10th motorized division was having to abandon a number of trucks, and 4th Panzer had only two days worth. The main difficulty, as I said, was getting things forward: AGC needed a minimum of 24 trains a day in order just to cover day to day operations and was getting an average of 18. It wasn't until late-September that even partial stockpiling in the forward depots could be conducted and these partial stockpiles were what the historical Typhoon partly ran*, and ultimately failed, on. Everything else was done hand-to-mouth, which worked out for lateral movements which didn't increase the distance from railheads remotely as much as a direct move eastward would have. Given this context, the supplies dispatched on the Leningrad and Kiev axis would have simply sat around in the main dumps just west of the Soviet-German border had they tried to be sent down to AGC. The German advance would be radically slowed by the fuel difficulties as they outrun their supply lines a full month ahead of time and what encirclements would be achieved would net much fewer Soviet soldiers, with the bulk able to fall back to the next defensive line and join with the forces there. You are correct that the rains merely slowed Guderian, as by the time they occurred Guderian was facing little resistance in his immediate path. And the Soviet replacements are easy to find: the Soviets had formed 13 armies in July and another 14 in August. Of these armies, 11 were deployed along the Moscow axis in multiple defensive belts stretching as far back as Kalinin and Tula. A 12th army was formed extremely deep, north of Stalingrad, and could conceivably have been railed anywhere. A 13th army formed between Belogrod and Kursk could conceivably have been moved northward with little difficulty. And the lone army formed in September was also formed in the STAVKA reserve and could have wound up anywhere, although OTL it wound up in the Volkhov Front in November for some reason. And on top of all of it, the Germans would lack a immense number of soft advantages they accrued from the extensive September pause, like the detailed reconnaissance of Soviet front line positions they garnered.
I see you also repeat the myth of pre-war formations Far Eastern formations holding the Germans along the Moscow axis. In reality, of the 14 divisions sent in the autumn, only 8 were assigned to the Western and Kalinin Fronts, which took part in the battle of Moscow. This out of something between 100-200 divisions that participated in the Battle of Moscow and it's easy to see that the bulk of the forces which halted the Germans in the end did not come from the Far East nor the pre-war.
*I say "partly" because they lasted less then a week, then it was back to hand-to-mouth.
Where do you think Guderian's supply lines were coming from? 3rd Panzer Group mostly fought in the area around the north wing of AG-Center except for 1 Corps that was sent to aid the attack on Leningrad, so it too drew it's supplies from AG-Center's rail lines. As the proposed move on Moscow would have had to happen in September, that would mean 4th Panzer Group would work in conjunction in August initially attacking and pocketing Soviet armies at the seam of their two army groups, while dealing with Soviet offensive action against frontally. Guderian could in the meantime clean up his flank somewhat and expand the Yelnya bridgehead. They wouldn't be using any rail and roads that any other troops were using or a-historical supply lines. 4th Panzer Group in their move east in August would be attacking the Staraya Russa area and Soviet forces south of Lake Ilmen to secure the seam of the army groups, then would strike south, filling the role of 3rd Panzer Group historically in terms of position as of the attack on Moscow, while 3rd Panzer Group would be in the center of the front; 4th Panzer Army could pull supply from AG-North's supply lines, while taking with it the majority of their truck supply so it could continue pulling from their area to relieve the burden on the Smolensk rail line, while AG-North would be on the defensive and stationary in the Baltic and along the Luga river line, so not needing nearly as much truck supply or rail conversion assets once they set their stop line for the year in August.
Initially a rail line coming off the Minsk-Orsha route. Even then, the whole advance was committed hand-to-mouth and encountered only a fraction of the resistance compared to what an advance toward Moscow would have entailed, which alleviated much of the demand. And even then it still, by Guderian's own admission, proved to be a close-run thing. In the end though, he indeed was able to draw off AGS when he had linked up with them. Guderian proved unable to clean-up his own flanks at the Yel'niya bridgehead for a solid month and his supply situation only improved when he pulled his forces back from the front for the transfer down to Gomel for the Kiev operation, which allowed his forces to restock enough to breakthrough the thin Soviet lines in that direction. As the Germans, by your own admission, would not be using any other road networks then what they used OTL and what they used OTL was inadequate to support continued offensives in late-August/early-September, it's pretty much going to result in a insta-logjam.
In the end, the forces AGC dispatched to other fronts, Guderian included, constituted but a fraction of the entire Army Group and by extension demanded a fraction of the resources that moving the whole thing would have required. It says everything that the greater part of the whole had to sit immobilized while all the flank battles were happening, which was a godsend for them as it gave them an opportunity to rest and refit.
Stahel and Glantz aren't really the best at what ifs.
Nah, they're great. You just don't like what the implications of their assessments mean for the result of the what ifs (even more catastrophic German defeat) so you claim their not great at it.
Depends how you look at the information. If you don't count the expenses of the flank moves on Kiev and Leningrad to AG-Center forces that had to relocate and still drew supplies mostly from AG-Center, while AG-Center itself was heavily engaged in combat for months with Soviet forces East of Smolensk, then I'm sure you can create a narrative that there wasn't enough supplies in place to have an offensive in September. The supplies were there, the supply lines they flowed in on were mostly AG-Center's and in any case for it's jump off point 4th Panzer Group would draw on AG-North's LoS at least initially, not AG-Center's.
The flank moves only used a fraction of AGC's forces, were much less demanding, and the rest of AGC's front was quiet for the majority of September. Additionally I should observe that the idea that the Germans could not take Moscow in 1941 in the face of the combination of Soviet resistance and German logistical difficulties is not just that of modern scholars, but also that of the German quartermaster staff before and during Barbarossa. To assert that the Germans could take Moscow in 1941 given their logistical difficulties and Soviet resistance, you are therefore not only flying in the face of current scholarship but in the face of the exact people. In this, you are very much following in the footsteps of the German generals at the time, who at best rationalized their quartermasters concerns away and at worst ignored them. I have remarked many a times in the past that you belong in OKH for a number of reasons, here is another one.
Considering part of that question is when and how that fight even happens, it is highly relevant to discuss whether it is the result of a Moscow offensive in August-September rather than October and having weather changes prevent the battle from even taking place. Also note I was responding to YOUR raising of the subject of an earlier push on Moscow, I didn't bring it up first. And talking about what ifs is now 'pontificating Wehraboo-fantasies'? Or is that only when they don't fit your Soviet-boo fantasies?
Talking about the end result of a early Typhoon that bogs down in urban fighting in western Moscow in October or November, which is liable to be the best case of a early-Typhoon, is very much in the spirit of the OP. If you want to talk about a early-Typhoon which actually takes Moscow somehow, probably by inducing a improbable but still possible panic among the leadership in Moscow, then start your own thread.
Budyonny was replaced in mid-September, but then he was Stalin's buddy, so got a pass for multiple fuck-ups:
https://en.wikipedia.org/wiki/Semyon_Budyonny#Later_military_career
By the time that happened his replacement could do nothing and Stalin had been warned about what was happening, so realized THAT was his fault. The fall of Moscow is altogether something different.
I'm still seeing no evidence of any purges that were initiated by any of the innumerable disasters suffered after July. Or in mid-'42 when the Soviets suffered a further string of disasters that at time rivalled that . While I agree that Moscow is altogether something different, Stalin would probably be the one most to blame if it fell (since it would pretty much require him panicking and flat out ordering the city abandoned) and would have his hands full holding together the country in the aftermath so I'm having a hard time seeing him kick off another.