I had the idea back in the time of the Conquerors expansion for AoE2 that Bohemian civilization should be included.
My thought was to represent the Hussite revolution and civil war in the game.
The idea was that when players reached Feudal Age, they would have two options for advancing to Castle Age in the Town Center.
The first option would be to proceed as Catholics, which would give them better economic and cavalry options.
The second option would be Hussites, which would give them access to gunpowder and wagons, similar to what Bohemians have in the game now.
In campaigns, players would be restricted to the historical requirements.
Additionally, I thought other civilizations could be represented in a similar way.
For example, Teutons could have Catholic vs Reformation, Lithuanians could have Christian vs Paganism, Chinese could have the ability to pick a dynasty, and Italians could choose a city state to represent.