I get all the arguments in favor of creating a world where WCs aren't feasible, but I also feel like creating a game where you can get a satisfying experience by hardly expanding outside of your historical borders is incredibly, incredibly difficult. Not because "if I cant map paint then the game isn't fun waaah" or anything like that, but because it's harder to design satisfying mechanics around "not failing", or "keeping pace of internal progression with other countries who also do the same" compared to just the very in-your-face act of beating other countries up and taking their land. This isn't me making a comment about some "objective fun" of either, just the challenge of game design as I see it
This is a wildly ambitious game, where a part of it being a successful release, will be if the players can find the entire 500 years satisfying, where currently in EU4 not that many players find the energy to play past 1600s.
I don't wanna make too many assumptions about how the game will feel come release, but I'd caution some people here from making many such assumptions either. All of this seems incredibly difficult in design, and I wouldn't be surprised if at some point letting players blob lots would be seen as just the simpler option, even if not an ideal one.