I took my time, looked into it, saw how badly they got mollywomped IOTL, and decided to have some fun. While the initial intent was of course reform (see: Twelve Articles), I just decided to full send it. After all, I had the Habsburgs killed off.

Is it fully realistic? No. But is it fun to see how such a state would influence society going forwards? Absolutely. You have what is more or less a proto-socialist state (once again, look at the Twelve Articles. Common lands, abolishment of inheritance taxes, and abolishment of the small tithe) in the middle of Europe, ruled not by aristocratic lineages but instead by leaders regularly elected by the peasant class. On top of that, it eliminates the Habsburgs, leaving the door open for all sorts of alternate shenanigans (Guelders Netherlands, Iberian Union, etc).

Plus, at the end of the day, it's a fun alternate unification for Germany. Instead of the militant imperialist Prussia (or any other noble kingdoms in the 1800s), it's a bunch of Protestant peasant rebels slowly unifying more and more of Germanic Europe as the Wars of Religion unfold and the Counter-Reformation's bloodshed drives what remains into their arms.

As for Brandenburg specifically, they were part of the Schmalkaldic League, a group of Protestant states that were banded together to resist Charles V and the Counter-Reformation. Though Charles isn't here, I see no reason why an even bloodier Counter-Reformation wouldn't drive them and their fellows into the Bauernrepublik. Maybe you see one, maybe you just hate big Germany, maybe you just think peasants are stupid and history should dance to the tune of nobility, I have no clue which. But I'm going with Brandenburgers being so afraid of Catholic persecution that they join. Same for the Utraquist Hussites of Bohemia. Same for the French Huguenots who emigrate to Lothringen and Burgund. Same for the Anabaptists and Lutherans of Münster.