Cultures: Serbian, Croatian, Bulgarian are added, and I also added Berber, Vlach, Wend, and tweaked the cultural setup across the scenarios.
Traits: Homosexual and patriarch are not included. It is possible to mod them in as I haven't used the user designed traits at all, but as I don't play with these I won't support it. Maybe if I can get some free time I'll try to do them as an optional addon though.
It is certainly possible to split up Russia in Novgorod and Kiev, but it's not something I've done yet. While I agree that Russia represents Kievan Rus', I feel it also stands for the later successor state -- namely Muscovite Russia, and I therefore don't think Novgorod ought to be excluded from it. This is not a final decision though -- I might change my mind later (but then only in the addon).
Combining DVIP and TASS on a scenario level is almost impossible -- DVIP uses a culture and kingdom/duchy setup which is compatible with the vanilla game (it is extending, not replacing), whereas TASS has reassigned existing cultures and redrawn the duchies and kingdoms. The tags not used in vanilla are probably used differently in TASS and DVIP as well.
Culturally there are the same problems (e.g. in CK/DV vanilla and DVIP: dutch = dutch; in TASS: dutch = frisian, and in TASS the three scandinavian cultures are merged into one whereas DVIP has kept them as in vanilla).
Our goals are different: Veld's TASS is about taking the game in a new direction, DVIP's focus is on improving the existing game while staying within the framework. You'll have to pick one of the two.
It might be possible to take DVIP events and put them in TASS or vice versa (I fully allow anyone to take any of my events or event edits and use them however they like), but in cases where tags or cultures are checked these will need to be checked for the mod they're being applied to. In general all events designed for the unmodded game will work as-is in DVIP, and any DVIP events should work as-is in vanilla.