They should really give spawn Tav/Durge appropriate spawn teeth if nothing else.

I don't think they will messing with skin tone just considering how many skintones there are in the game, and adjusting a paler version to each of them would take a lot of work. They can always make it so that the paleness just doesn't happen immediately in their lore, and that's why spawn Tav doesn't have it yet. The eye color change could be dealt with by dividing the existing eye colors into three categories -- light, medium and dark -- and then just selecting a red for each category; this way those who want their character to have heterochromia can still keep that aspect, assuming they've chosen colors from different categories. If not... well you did decide to become a vampire spawn so you'll just have to live with the changes.

Also they should remove Tav seeing themselves in the mirror. It's not even a big change. The reason I think Larian might not do this is because that would require them to call the voice actors in for new lines, and I don't know how willing they're to do that for a small immersion thing. It's a shame that they probably won't do that, but since they did give us the ability to become a vampire spawn, they should at least do something with the immersion.

At least give us the teeth, Larian. You get cosmetic change if you eat the forbidden gummy worm, why not for this?

As for the lack of any interaction, rp elements or even basic reactivity from anyone... yeah they should definitely change that. Like the bloodlust (if you're supposed to have that pls Larian clarify if Astarion is blocking that one too along with giving us sun immunity) could very easily be implemented by copying the way it was done when you play as Astarion; when you recruit Shadowheart and Lae'zel you have the dialogue option to just zone out and contemplate how much you'd like to bite them. They then react to your zoning out. This could be a relatively simple way to implement it in camp dialogue or something with Tav. If they really wanted to go in with it, they could make it into a game mechanic where, if you don't bite anyone, be it friends or enemies, and you long rest, you get a debuff similar to the bloodless status that you can cure with the bite. That way you'd also need to play around being a spawn. I do realize this is something we'll likely never get, though, and people might not like it since it would force them to engage with the bite mechanic quite a bit.

Also we need the companions to at least comment on you becoming a spawn with one line or something, even if we can't have a full discussion about it with them. They should have opinions about it; you're supposed to be their friend, and they have opinions on every other companion after something happens with them. Then again they don't care if Durge
quite literally dies in front of them
so maybe it's in character for them to not care about this too.