would be amazing, BUT i would like it when it would contain the current eu4, hoi3, vic2 gameplay cause you CANT make a gamplay fits to all. so let me explain what i mean:
You start playing with an certain Interface and stuff, some things and Options unlock within the next 200 years, THAN when a certain date is reached, your ENTIRE UI changes and you get entire new Options/economic/war System. Like this: imagine you are in 1200. Then you have a gameplay ui and style similar to crusader kings. Once you pass the end of medieval Age, your Ui changes and you get another System, similar to eu4. Then when you pass another important date again, like 1701, you get a System like in Vic2, where you can build factorys, although you have to unlock it first and not ALL of the new ui is aviable at start. When you reach 1900 you get a ui and Options like in hoi3 (theatres of war and stuff), to make it possible playing with ww1 techniq.
Neverthenless, the map should have hoi3 size all the time. And to make it POSSIBLE for Paradox to complete that game, you can only start a game at cetain Benchmarks, additions would be Benchmark dlcs or mods. I would say 1 Benchmark every system Switch and before every important huge conflict. So i think for 3000 years of time (estimateing 1000 BC to 2000 AD) around 50 Benchmarks.
Of course the UI Switch would happen faster, if the Nation you Play develops faster, for example would China Switch much faster to eu3 like UI and gameplay, than europe, if it doesnt destroy hist fleet and go for Isolation.