But German nationalism won't disappear just because the Allies decree it, and the Germans will try to reunite themselves as soon as Allied armies no longer try to stop this.
Just look at OTL partition: The allies signed a treaty on Oct. 2nd 1990 suspending the enforcement by midnight the same day. I'll leave it to the reader to find out how long the unenforced partition lasted

.
And the Allies are not likely to have the will to balkanize Germany. Britain in particular wanted it to be reasonably intact.
That's why OTL ToV failed so fast: France thought that they were now officially the only superpower in continental western Europe and Britain was obliged to enforce it, and Britain didn't want aid French domination any more than the German one.
IMO the only parts of Germany that can plausibly remain separate for any significant time are areas near the Rhine (France might still be willing to use force there, if nowhere else) and East Prussia (Polish concerns and the region's isolation from the rest of Germany). Maybe a more successful communist revolution leads to a civil war which ends in a stalemate, but is it realistic for both sides of a civil war to maintain similar strength for a long enough period that both sides decide to give up and recognize the stalemate?
Bavaria can be split and given some additional territories, perhaps all of Baden and Württemberg. The Rhineland might be independent as well, and since East Prussia has no land bridge to the rest of Germany, one might try to seperate them as well.
But the hard part is: How do you get Bavarian/Rhenish consent to keep the balkanization permanent?
IN OTL, they were after all able to avoid Austria joining Germany until Anschluss.
But they failed to avoid the Anschluss, didn't they? Besides, (German-)Austria left Germany in 1866, not 1918.
Maybe they could let
Altbayern join Austria?
Another interesting option...
Also, France, or maybe Belgium, annexing areas around the Rhine would seriously weaken Germany.
There is a critical mass: If they annex too much, they trigger German irredentism and loose credibility among the rest of the Entente.