You have multi-million dollar projects that don't do this because it's too difficult.
And yet expect that some open-source project gets there?
I'm not saying it can't be done in theory. But I'm very dubious about whether it reasonably be done. CK2 is already a huge abstraction with mechanics that especially towards the beginning and the end of the era, plus in certain regions that aren't quit feudal Europe, stretches what the system can do. EU is even more abstract and only works for a certain time period and again, it doesn't make sense everywhere equally. Vicky II was pretty good for the Victorian era, but it's completely different from CK and EU. And HoI covers basically WWII only (although WWI is kinda doable) and is again completely different, and I have no clue how such a game would look in the Cold War or modern era and still make sense.
It kinda works for games like Civ (or Empire Earth or whatever
) because they come with abstract systems like "epochs", they aren't particularly historic and their scope is such that the gameplay is vaguely representative of what's going on. But drastically changing the rules and gameplay systems and so on in the middle of the game, gradually, for every country individually, and with some historical accuracy? Plus, although the Paradox Games aren't meant to be perfectly historical, they are meant to be at least kinda based in history, and if you start 780 CK games, history will already develop totally differently from the historic outcome. It's 700+ years to the reformation from there! So stuff you might like because they are historical - like the Holy Roman Empire and 30 Years War - can't easily be done anymore, as there's no way to predict how a game will go.
So if such a project were to be attempted, I'd say it would have to be some fantasy scenario. That could be constrained by some fantasy rules to nudge it along a certain path that limits scope to something that maybe can be handled in some way.