Things that EUIV needs:
1. A better colonial system. The current one as it is just bogus: Bunch of guys migrate, colonize, when they reach 1000 all the natives magically see the superiority of their colonizers and convert to their culture and religion. Positively Derptastic. They need a system that does the following:
a). Missionary efforts to convert local injuns (especially Jesuits). They were quite important and involved many people, natives and missionaries.
b). Interactions between locals and colonists in fun and interesting ways.
c). Small outposts that exist only for trade IE bring back trade posts from EUII. One addendum I would make here is that a trade post should't control a province, rather, they should work somehow like the trade posts in CKII's republics. A cool idea would be to also allow foreign trade posts inside other nations' colonies, to represent smuggling. This would also be a awesome way to represent the trade between african slave seller nations and european/arab/ottoman slave buyer nations. Portugal should't have to pay lots of jewgold and build a city só they can get themselves some niggers to work on the sugarcane plantations. Lastly, European (and perhaps Chinese?) powers should also be able to build trade posts in India and use them as bases for the kind of european-indian fighting that was going on.
d). The undeclared war going on between colonial powers. There was a lot of undeclared fighting going on the entire American continent, especially early on when estabilished colonies were but a few, nobody recognized and respected each other's claims (even the Spanish and the Portuguese ignored Tordesillas often) and the metropolei didn't know half of what was really going on in the continent.
e) A colonial system that represents all colonial types – Extractivist colonies, settler colonies, military outposts, trader colonies, etc.
f) Represents properly the conflicts going on between colonials and the natives. Doing deals with friendly tribes and raising native auxiliary armies, fighting local encroaching natives, proper consequences of native genocide, possibility of natives fighting back, etc.