Here's an interesting idea. Say the Spartacist uprising in Germany in 1919 succeeds, maybe with a dual PoD. The first PoD being that the SPD decides to support the revolution wholeheartedly, planning to act as a moderating influence post-conflict. The second PoD being increased radicalization of German soldiers in the trenches during the war, leading to a weakening of the Freikorps and the defecting of some "National Socialist" Freikorps to the Revolutionary side. In this scenario, the leadership of the German state manages to flee to East Prussia, where under Ludendorff they establish the Imperial State of Germany, with a "government-in-exile" at Konigsburg.
Is this plausible? If so, what would the social and economic situation of East Prussia look like? How would their relations with their neighbours be? How would the Western powers treat them?