Everyone seems to be ignoring how, much as their interests often contrdicted, Austria and Germany pretty much acknowledged after 1871 that they wouldn't, couldn't directly quarrel. For both sides, the Austro-German alliance was a pillar of domestic support from the pan-Germans (who were collectively the third faction in the Reichsrat) as well as, and sometimes more than, an entirely calculated foreign-policy choice.
Austria had enough domestic troubles as it was, what with the, ah, abrupt end of the Stuergkh regime, and the Social Democrats and Kaiser Karl trying to conspire to make peace and all that. I can hardly see how she would weather one defeat without outright mutineering.
So, if Germany really justs need to send a shock-army down the Danube hullooing before Austria starts to fall to bits, I really don't see how the Austrians are supposed to last.
Germany has eight or so armies to play with. To attack France with a vast, bold, risky manouvre was thought necessary to crush the French before the Russians could mobilise. If Germany and Russia are best buds, this is of course unnecessary, so Germany doesn't need "the same forces" against France: it needs three armies, tops, for the French to bash their heads against ineffectually while the bulk to the German forces are free to utterly compromise the lengthy Austrian border by their superior numbers and take Prague and Vienna as the Hapsburg state topples over.
The Austrians, with six armies in 1914, managed to not defeat Serbia while simultaneously being defeated by Russia (it was German pricks elsewhere that halted the Russian tide in Galicia). They weren't bad soldiers , they were just stretched to the limit of their resources by two fronts. Three or four, including a domestically disastrous one that happens to be too long to defend effectively, is right out.
The Ottomans will indeed have a vastly improved logistical and troops situation, but the Russians have at least a couple more armies going south. The Caucasus favour the defender, so I predict it will just settle down somewhere not terribly far from the pre-war frontier to either side. Eventually, the Russians can just throw everything south, and damn, there are a lot of them; but by that time the *Entente will probably be looking for terms anyway.
Britain has six excellent divisions, and needs time to mobilise anything else. Where do we send them? To a France which will shortly have the entire German army coming down on it like a ton of bricks, while the Italians possibly help themselves to a share of the spoils? Probably (the French considered it a political gesture), but I doubt it will do much good to anyone.
The Germans and Russians frankly can't lose. When you take the continent's two top land-powers, with the biggest and the best army in the world, which in OTL spent all their time being scared shitless of one-another (diplomatically as well as domestically, this scenario is supremely unlikely: Germany and Russia are perfectly capable of building a working alliance, but it's hardly likely when both of them happen to be reaching peaks of their power that made other people a bit jittery), and have them to take on everybody else, that's the expected result.