In 1928 the
Bund zur Erneuerung des Reiches (League to Reform the Empire), headed by the former chancellor Hans Luther (which is why some refer to this organization as the
Luther-Bund), was a movement to reform the Weimar Republic in a very substantial way: a partial end of the federalism which dominated German politics up to that point and, excluding the Nazi dictatorship, continues to play a big role to this day.
This was supposed to be done by turning Prussia, potentially including many if not all smaller German states which used to make up the old North German Federation, into what they wanted to call a Reichsland, which would not have a distinct state government but would instead be governed directly by the national government. This Reichsland would still have provinces like the former Free State of Prussia, which would however have only minimal levels of self-government but which would be represented in the Reichsrat (the Weimar equivalent to the imperial and modern Bundesrat).
Only Saxony, Bavaria, Württemberg, and Baden would keep their own state governments and their pre-existing privileges.
While the Luther-Bund had several prominent supporters, including Konrad Adenauer, there was no broad base of support for the proposal, which by some has been compared to the current state of devolution in the United Kingdom.
Here's a very quick WorldA patch for the proposal using the territory of the Weimar Republic in 1928.