This is something that requires a lot more follow-up, and is granted MUCH more limited in scope than the other scenarios, but still I think is something that doesn't happen nearly enough in actual gameplay: a 1900 scenario map, with defensive pacts already set up and auto declaration of war in 1914 to trigger the Great War and another in 1939, if not still at war and if Prussia is still alive.
It would be intended for UHVs like Japan, America, Prussia, Russia, etc., but also would be for other late game victory conditions like Technological or Domination. I also think it would be cool to see city placement with historical colonization and imperialism already set up. You could end up with plenty of different alternative history scenarios following the Great War, like where Prussia wins, where France or England are able to maintain their colonial empires, or where Prussia is completely wiped out and WWII is completely averted.
If there is any interest in this, I would love to work on this personally.