I have pondered a stalemate WWI that results in an unstable Imperial Germany, Kaiser and Crown Prince abdicate in favor of the next in line under a Regency, the Social Dems with the Centre assert political dominance in Reichstag against an antagonist but weak fractured Right, revolution still sparks off but gets put down by "legitimate" Government and Army. Peace terms are regarded as unfair but not actually harsh until later revisionist propaganda twists it. A-H succumbs to revolution and Nationalism, Allies frustrate German intervention and any union with rump Austria. The Austrian party that became the Nazi's prototype and inspired the NSDAP (from events in Italy) goes ultra-nationalist and Pan-German.
In such a world I can see latent Bavarian independence feeding the original NSDAP to a serious player in the Kingdom, especially as the SDP likely asserts itself, the Austrian counterpart sees Union with Germany as its siren call to set itself apart from the competing Right in Austria, especially as Italy continues to be an enemy to Austria and those opposed to Union increase ties to Italian Fascism. The SDP and Centre are favorable, conservatives oppose but the NSDAP follows the Italian example and goes very hard in favor of Monarchy and Union to edge out the Right. I see the Bavarian Nazis at deep impasse with the Bavarian government and its ideals of independence from the Reich yet sympathetic for its calls to bring the Austrians into the fold and support for the Crown. Hitler and his crew are vocal rabble rousers and go farther than they should as forces use them to offset the Communists and propel Pan-Germanism.
Thus I wonder if Hitler remains in Austria or goes to Bavaria? Does he work in reverse from Austria to attempt to gain control of Germany as a whole, leveraging "Unity" and feeding the resentment over the lost war, aggravated by the likely still bad economics of the 1930s-era? So perhaps Hitler and his gang still have a place in German history, but with a surviving Monarchy I see him at best getting to an Il Duce level beneath the legitimate Crown and so long as he can deliver on law and order, prosperity and putting Germany back into the Sun he has great latitude. Yet I suspect a war with Italy, an era of anti-Semitism, mass mismanagement and finally the potential for war with the resurgent USSR, likely over Poland or possibly Romania. It isn't quite unfettered Nazism and it likely ends with the Army crushing the Nazis once he gets Germany into a losing war, but I can postulate how they still manage to claw up from the gutters and grab power.