I honestly love EU4 to death, but I can see that myself that it's not going to be sustainable for too much longer. There are so many superfluous mechanics that most people, outside of the hardcore sweaty min-maxers, don't use.
I think EU5 could be a great opportunity for a fresh start if they build on a lot of the base mechanics like CK3 did. The problem with CK3 is that although it's a solid base, it feels less flavoured than CK2, which wouldn't be an issue in and of itself; however, the development cycle for the game has been painfully slow and after almost 2 years, not much has changed and I can't say I'd rather play CK3 over CK2. I personally fear a similar situation.
I personally believe though that There'd be a conflict as to what people envision EU5 to be. Some people want it more simulation like, but others like myself, would prefer it to play out more historically, without player intervention, but still be very reactive and alive, something similar in spirit to EU4 with its DHEs but expanded. I could see arguments for other the side too, but I personally don't feel every game needs POPs and I don't think the simulation would hold too well over the long time-frame of the game and still produce something resembling the real world situation. Then there are people who argue for a short game, since most don't play that late into game and I can see the reasoning. But I could also see that instead of cutting the length, they could add more depth to the late game, with changes in mechanics and make empire management more detailed and difficult to prevent the late-game snowballing that makes it too easy and boring. Although fun and not arbitrarily punishing anti-snowball mechanics might be hard too... and the debates can go on and on, and not everyone will be happy at the end.
One thing I don't really want at all is a 3D character model system. I don't know why, but paradox has felt the need to push and I feel it's not needed at all. The one from I:R was perfectly fine and I certainly don't development time wasted on a DLC focused on this nonsense, when there are far more pressing matters (see: CK3 Royal Court).
I'm a bit worried, if not sceptical, but id defi keep an open mind. I could definitely see EU5 doing a better job at trade, culture, empire management (and collapse) and importantly colonisation. If it launches with flavour and mechanics for all the big actors of time period, it'd definitely have a very sturdy base with great potential. I understand the corporate need for growth, but I also just hope they cater to the existing fanbase first, as they are the reason the previous games' success.