Having read the article about the expansion, I'm not so sure on the features anymore. To be honest, while the article offers more insights, it is of course not super detailled, but still, some things don't sound that great.
Firstly, I know, its somewhat nitpicky, but still. In the article it says
"You will be able to view the throne room, which acts as a "glorious bridge between the map, on one hand, and the character, on the other," from different angles. It will be stylized to fit FOUR different cultures"
I know that you cannot make visual distinctions for every single culture. Obvious. But seriously, why four?! I cannot find a way to group the world of CK3 into four visual areas for these purposes, at the very least, if you simplify everything, you'll need: European, Steppes, India, Oriental, (Subsaharan/East)African. That's 5! Come on! Not to mention that a few more distinctions would be really nice (i.e. northern/central/mediterranean Europe).
I think grandeur is good. Depends of course on the balancing; how easy it is to get to 100 and how much you get for it and there's a lot of potential to screw this balance off (cough, dread, cough), but it seems like a good way to a) create a large money sink and b) introduce artifacts without insane stat bloat.
Introducing languages also looks great. Speaking the a common language definitely makes a huge difference when it comes to personal relations. Not sure why it's a scheme though (I guess personal scheme), seems a bit weird. And the whole part with "if the person you learn the language from doesn't like you, they'll teach you wrong words and stuff" sounds a bit too silly. I guess we will have situations where the king of england asks his rival the emperor of byzantium to teach him greek but he will only learn mean words, haha so funny. a) Neither travel nor transport where that advanced in the medieval period and learning a language requires communication on an almost daily basis; b) a ruler would probably not teach some other guy from somewhere else his language -> rulers learned other languages from tutors. Of course there are exceptions where it does make sense (same realm and next to each other, neighboring and related, vassal in lieges court, guardian, spouses) and I hope that the feature will be restricted to such more plausible options.
Holding court in your throne rooms seems nice and we don't know a lot about it. I think it can be a good addition, yet it has to be careful to not feel like a repetitive event lottery. Also, some of the announced features (negotiating peace betwen vassals) should not be based on some RNG event, but be actual mechanics with actual negotiations taking place (don't even mention the "stop vassal war/ waste prestige button" we currently have).
And then culture. Firstly, dynamic cultures is good. Vikings invading india, would probably have some consequences. But, in my opinion it looks like it will be some "you are the cultural head so you can click this button and change your culture to be more Y if you have enough prestige" feature, which I don't like. Similar problem as with cultural heads, although more problematic. Doesn't make a lot of sense. Same goes for the "cultural divergence" button that we will get. Just because that one king says that now everyone is of that new fancy culture with his new madeup name and he spend a bunch of prestige for that, why should that all of his realm?
Cultural acceptance is again, a good idea in principle. But in practise, I think it will turn out quite underwhelming and suffer from many illogical situations being badly represented by this system. Being primarily driven by war/peace a lot of cultures will just hate each other, just because well, the AI likes to declare wars when it can. Do all wars count? With all the internal rebellions, I'm sure everyone hates everyone by the end of the first decade. And then, what if the (for some weird coincidence - happens all the time in this game) french king of southern england declares a war against northern england held by an english character? Will the english peasants now like the french less? Or the english? Probably the french, as they are in charge, but what if all his lords and knights are english? Doesn't make a lot of sense, right... And if the french king of england fights the english king of france, all the common folk will just be totally confused.
Furthermore, it kind of assumes that all english, regardless of where they live, are this kind of unified cultural entity. But if the french, with the help of their allies the northern english attack the southern english, I don't see why that should cause the northern english to loose opinion of their allies just because the southern english don't like to be invaded.
Don't take me wrong, I can see where the idea "fight wars -> culture relation gets worse" comes from (the english and the french, what a coincidence). I'm just sceptical because I think it will create too many situations where the players intuitive judgement of the situation does not match with the games mechanic, which I find super frustrating.
Also, I think there are some other factors that could go into this cultural opinions. For example language. We've got quite a lot of cultures on the map that do speak the same language (or at least a language so similar, that they can understand each other decently). With languages evolving over time now, this might provide a way for cultures to come closer together (without some godlike random buttons).
Finally, more court positions. I love that they introduce a salary. I've always wanted that back in the days of CK2, I tried to mod it into CK3 and I love that they now make it a proper feature. I just assume that it will also apply to councillors. Making these positions actually matter is of course the best part about it. But I expect to get regencies too!
TLDR: I'm very sceptical about how the cultural changes will work out in game. They seem to be very character focussed (click button and spend prestige -> your realms culture diverges/changes) and might from time to time create unlogical situation (french king with english lands & vassals attacking someone -> they hate the french). Maybe it would have been better to just make more character focussed mechanics - for me the trailer felt like this DLC would introduce more detailled wedding negotiations, promises and more court intrigue (minor titles), but well, maybe they haven't announced them yet.