It would have been a valid approach to the defense of the Reich. Asuming Hitler can somehow be convinced of picking this strategy, I forsee the following scenario.
The plan lets us hope for more efficient defense, in exchange for the loss of long term advantages, which is a fair tradeoff given that short-term survival is at stake. Higher losses for the allies and the soviets attacking Germany, probably less german soldiers gets taken prisoners, and therefore more manpower is available, allowing Germany to stay in fighting shape longer, as long as stockpiles hold.
Because of this, Soviet offensive runs high risks of collapse. The reds were historically nearly exhausted, and would probably refuse to march on if their homeland is freed and if they keep taking heavy losses, with the Oder still nowhere in sight. The German situation would be pretty bad, though, so they'd lose either way. So ether Stalin sees this and waits for the western allies to finish his job, or he goes for the other approach, and signs a truce with the germans that lets him gain as much as possible.
I think the latter approach is quite likely, as this fortress Germany will put the emphasis on its eastern defense. So, according to the terms of his own treaty of Brest-Litvosk, Stalin gains a good chunk of poland, leaving German-annexed parts to Germany (for now), but he also gains hegemony over Rumania, Bulgaria, Yugoslavia, Slovaquia and Finland. This leaves Germany without the ressources they need to fight in the long run, but the Germans agree to these terms as their alternative is to leave their western front hopelessly under-defended. The critical battles are also all due in the short-run. An exchange of prisoners that takes place afterwards also boost German manpower. Lets say this occur early in the year 1945.
The west has still a crushing military superiority over Germany, and theyll definitely win the war, either by nukes or by conventional invasion. The Reds probably realized that, but they needed to stop and reorganize or see their front collapse. Stalin is quite unwilling to let the allies get all of Germany, and might attack again should things move in that direction, with fresh armies of course.
Germany of course move all its forces westwards to defend the border, launching a couple of semi-successful counterattacks ala Ardennes. One of the most successful aspects is the concentration of the remains of the Luftwaffe's fighters to protect the german cities from bombing. The late-war luftwaffe does much better at the task than before, saving countless civilian lives. Hitler's grasp on power is strengthened by his peace pact with the USSR, and he manages to fight on past his OTL death. But late in spring, supplies run critically short, and the Soviets refuse obstinately to sell any to the Reich. (Though some gets smuggled from remaining Balkanic sympathisers, I suppose). Northern Italy is overrun and allied armies marches both on the Rhine and through Tyrol. As defeat looms, another assassination attempt on Hitler fails on the anniversary of the Normany landings, which drives the angered dictator to order more purges. This time, though, he overestimates the scale of the plot and orders too many people shot down. An SS commando ironically assassinate Himmler while another (more loyal, or less depending on the point of view) enters the bunker at gunpoint, killing the Fuhrer and creating another "stab-in-the-back" neo-Nazi fantasy.
Doenitz restores order quickly with the support of the military. Contacts in Sweden and Switzerland leads the German officials to hope to achieve a separate peace if the Nazi leadership vanishes. Several personalities too closely associated with Hitler vanishes. Doenitz makes private calls for an armistice, trying to negociate territorial integrity, especially in the east, in exchange for allowing limited allied occupation. The allies are not satisfied with the first offers, especially with an A-bomb so close to completion, but for now, the regular bombing of german cities stops, a sign that the allies probably believe peace is very near.
But while resistance remains stiff on the Rhine, the newly-crowned german leadership is increasingly accomodating in its terms of surrender, its increasingly difficult to make a case for the use of an A-bomb. (Still uncomplete, anyhow) In the east, however, Stalin begins to fear that the allies are about to give up on unconditional surrender, and leave Germany intact, which does not fall well into his calculations. He hastily plans a renewed offensive.
In the west, the german lines are critically short on ammo, fuel, and morale, the allies have managed to cross the Rhine, and troops are too busy with the interior situation to oppose a continued allied advance. Therefore, on the 10th of July, Germany signs an Armistice at Mainz, recently taken by the allies. The terms are not Unconditional surrender, but they remain harsh. There are some hopes for Germany, though.
They grant legitimacy to Doenitz' temporary military government, but place the security of Germany (and therefore allow the occupation of) in the hands of the allies - the *western* allies, specifically. More annoying for Stalin is that the armistice promises a certain amount of territorial integrity to Germany, and promises not to tear it piecemeal. The re-creation of poland is a condition as well, though Soviet withdrawal from its own part is a pre-condition, a last minute concession. The most important clause is "All German resistance is to stop immediately on the western front, on land, air, and sea". Of course, lands west of the 1937 borders are restored to France immediately, Luxemburg is re-created, and Bohemia passes under allied protection, though for now confined in its 1939 borders. Other territorial details will await a peace treaty.
The main problem emerges behind the scenes as Stalin learns he is not to annex everything all the way to Berlin. In fact, according to the terms of the armistice, he is not either to be granted an occupation zone in Germany, a main German condition to allow unrestricted British and American occupation and "De-nazification".
A critical three weeks go by, during which diplomacy between the western powers and the soviet bloc becomes quite heated. Truman, unlike FDR, sees reason in Churchill's stance that it would be foolish to let the Soviets swallow central Europe after they bailed out on the alliance early. He furthers support that position given that he had angered his british ally by renouncing to Unconditionnal Surrender, which Churchill favoured.
Stalin, on his side, knows that Germany is almost beaten in front of his armies, and believes he can expect that there wouldnt be too much allied resistance to an assault on Germany if he didnt cross the Oder. But as he is about to carry out his plans, Hiroshima explodes in flames. The German ambassador to Kyoto is immediately recieved by the Emperor and convinces him to demand an immediate armistice, not matter how harsh the terms. The second nuclear blast never happens, and peace is signed with Japan a week early, even though they still hold Mandchuria (No soviet attack) when they surrender inconditionally. The only difference is that the treaty bears a formal guarantee to respect the Japanese Emperor and not accuse him of any crimes.
The German government meanwhile is hard-pressed on all sides to restore civil order, explain to the people the crimes of the previous regime, support a substantial occupation army, trade prisonners of war, help with "de-nazification" while preserving its own credibility, and many other things. But Doenitz is still nontheless aware of the threat of an imminent soviet attack on East Prussia and german poland. The current Germano-Soviet border is slightly more favorable to Germany than it was in 1913, and after such a bitter war, the pill that it could remain such is hard to swallow in the Kremlin. Much of that land is supposed to be given back to a free polish state, but Moscow shows no signs of being willing to hand over it's part, written condition for such a retrocession to occur.
Though the German army had been largely disarmed by the occupation powers, order east of the oder is still largely assured by fully armed German soldiers. In fact, to avoid complete capture of the war arsenal, many planes and tanks were shipped east once it began obvious that the allies cared little for what was beyond the Oder. This attitude was one of the main factors that makes Stalin think he can pull a fait-accompli. The WW1 phenomenon of free-corps ensuring eastern defense appears again as veterans organize themselves to protect the eastern territories. Though there are delays due to the developments in Japan, Stalin launches his juggernault against Germany on August the 31st, 1945. Right away, at the border resistance is pretty stiff. Freecorps rapidly organize guerrila operations as professional troops are gathered around Tannenberg as a rallying symbol of resistance. Many Germans now realize the horrors of Nazism, but they still hold no love for the bloodthirsty, and revenge-driven communists in the east, and for them, this battle becomes a way to salvage the national honor after two large scale defeats in 25 years. Of course, the country is in no shape for a real war.
But in Berlin, Doenitz' government calls frenetically for allied protection, invoking the security clauses of the armistice, but the allies do not seem willing to make a move to protect the far-flung polish territories. Calling upon the fact that the armistice demanded only the end of the resistance on the western front, Doenitz orders all available soldiers to take back their weapons, and fill trains bound for Prussia. In some places, friction appears immediately as German troops enter small conflicts with occupation forces to gain control of weapon storages, including a famous incident near Munich where 60 spitfires are stolen overnight from a major British airfield in a commando-like operation and flown east by ex-luftwaffe pilots.
By the time the allies react, almost all the German armed forces are east of the Oder, and the fight is raging on. The only solution of the Allies to restore order is to cross the river themselves as they fear a resurgent German military that takes too much freedom. But by doing so, they are forced to commit themselves increasingly to police a conflict they had thought would be limited to a quick Soviet fait-accompli. In face of staunch German resistance, Washington condamns the soviet assault formally on September 15th, and proclaims on the 22nd that Germany's eastern borders would be defended until the re-creation of a democratic poland. Allied forces, sometimes under contradictory orders, clashes at a few keypoints with the soviets late in the month. The largest of such incidents turned out largely fictional, as fiercy anti-communist General Patton, largely overstepping his bounds, sent a telegram magnifying his small operations into large scale victories and requesting more troops to push back the soviets. Nontheless, the telegram stating "Trapped six soviet divisions between Kutno and Lodz, requesting additional reinforcements to finish the assault on Warsaw and permission to arm German irregulars." scared Allied Command so much that it marked the last day of the conflict.
Rightfully fearing a spiral of escalation, the Allies intervened politically in force, demanding an immediate return to status-quo ante bellum. Faced with few alternatives knowing the extent of the american arsenal, Stalin withdrew bitterly to his July borders, proclaiming in the process the creation of a diminutive "Polish SSR" over the ruins of the old German's "General Government of Poland".
I think I could write more, but Id like to have your opinions on the plausibility of this scenario first. We have a pretty different cold war ahead, with central Europe much more on the allied side, but with Germany politically stronger, though with a very restricted margin of maneuver for now. And of course, with a very bitter Stalin all willing to accelerate his nuclear research to avenge his humiliation.
