I think this "most factions feel the same" feeling is still the case, because the updates are just focusing on mechanics, which are for all factions the same and while we received a couple of faction DLCs, they only adress the greek world (plus Rome and Carthage, but their missions are pretty generic conquer missions).
1. Imo it would already help, if the three main government types receive more love (especially tribes and to some extent monarchies, republics need some more refinements - and some further content would be of course also nice). Some more differences between the subtypes would help even more.
2. Next we need some flavour packs = the mission packs need some more flavour for the culture group it focuses on like the flavour pack from CK III, where you get some unique content for the vikings by adding and changing stuff to/from existing features - this becomes in I:R more and more a thing, because we get more and more deep and interesting features, which should vary in smaller parts.
3. More diverse events, character portraits, character backgrounds and maybe even UI looks for the culture groups. Maybe these should be seperate small DLCs, so only people have to buy them, who enjoy this stuff like me. Currently all barbarians or greeks or eastern factions or indians, etc. doesn't have a lot of diverse looks within them and you often see the same clothes, hairstyles and even facial types (there are minor differences between every face, but they still look pretty similar).
4. Buildings based on government types and/or culture groups for more diversity in city and settlement management. But before that, we first need an enhanced version of the current building system (there are already a lot of threads about that)
About the overall game: Things like trade, diplomacy, subjects, internal politics, naval gameplay, etc. hopefully get an update aswell, because these things still aren't in the best shape, which is the case for EU IV. If they receive updates, they will exceed EU IV and I:R finally will be the better game overall. So EU IV has the advantage of already having so much updates, but I:R has the greater potential, but potential needs to be used.
But as long as Paradox supports I:R, I'm optimistic that the devs will make the best out of I:R
