I don't really see how they could do a sequel to EU4 or CK2 without them being a massive step down in terms of complexity and features.
How can they put something out the gate that matches, on day one, the years and years of patches and DLC that have gone into those games, with a budget within the realms of sanity? Because if you think fans are going to be understanding of that... well, they won't be. Stellaris is in a bit of a different place right now because the past two years have largely been about working out what type game they want Stellaris to be, and redoing much of what didn't work in 1.0 but given another two years it's going to be an absolute beast of a game.