Theres a few things i would want PI to consider with an EU IV.
1. I think it would be cool to have family trees, with your dynasties. You could see exactly how your royal marriages are. This would also make it a little clearer about who would inherit who and so on and so forth. I also think picking your heir would be nice. Overall kind of like Rome total war except more in depth.
2. More provinces, much like the MEIOU map, except more. More is always good.
3.maybe an even earlier time line. I cant see paradox shrinking the time line from what they have now since they know it works, i kind of would be disappointed if they made it shorter. Thats why i bought EU III over HoI, there was more playtime.
These are just a few ideas, but i would wait in line to get this.
Welcome to the forums! Anyway, dynastic trees would be a good addition, but being able to pick one's heir doesn't really fit the timeline unless you adding succession laws that could be changed. That however is a little too complicated for what this game should have and the entire gameplay of Crusader Kings is based around huge family trees. I don't think EU3 should encroach on CK territory. The other two suggestions I don't really like. More provinces means a more powerful country and should be used to represent densely populated countries. MEIOU does that; any more provinces would have to be added across the board and would be largely unnecessary. The timeline for EU3 is stretched as it is, and doesn't represent the beginning and the end of its timeline very well. Besides extending to 1836 just to link with Victoria, I wouldn’t support any timeline extensions in the official game. Besides, mods for EU3 can do it already.