This may require a pre-1900 PoD after all but I'm wondering, perhaps in a different WW1 or a different aftermath to the war, if it would be possible to create a kind of Catholic little-Germany out of Austria, Bavaria, and most of the Sudetenland?
It seems like greater German unity was on the mind in Austria at that time and this may be palatable rather than creating a new super-Germany. I figure the most likely way to have something like this occur would be a greater partition of Germany after the war, itself I'm not sure is super possible
Post 1900 it would be extremely difficult to do as German nationalism would be so strong that even if you somehow made a Catholic Kleindeutschland, it would be extremely difficult to keep togeth (e.g not be reabsorbed by Germany). Pre-1900 becomes a lot easier to do but if you want a post 1900 (though somewhat unlikely) one here goes:
1914: The German's recover from their setback at the Marne quite a lot better, keeping critical ground and almost win the race to the sea, but aren't able to knock France out of the war.
1915: Gallipoli never goes through with thousands of troops being redirected towards the Western Front.
1916: Falkenhayn's plan for Verdun almost works, draining much of the French army, however with extra troops from the cancelled Gallipoli campaign, the Somme Offensive is initiated earlier throwing the German's off balance and create a real crisis for the German's.
1919: The British blockade brings Germany to her knees and an even more drained France goes through with her plan to rip Bavaria away from Germany. Due to providing much more support than IOTL, Wilson is able to convince the Entente to create a South German state with rump Austria with the ethnically German South Tyrol and Sudetenland. Pressburg Oedenburg (Sopron) join this new German state through a referendum.