I think that deciding if Tav/DU has any kinks should be decided by the player. I do understand that many people here would enjoy being a sub and should be allowed to do that. Other players don't and should be allowed to choose that. Deciding if Astarion, spawn or Ascended listen to Tav or DU preferences, kinks or vanilla is up to Larian. Also, some people might be doms and not subs or switch. Or have some kind of boundaries...
How to code the choice might be done by dialog. For example, when a character offers Astarion to drink their blood, is a good moment to mention if you are into masochism. But it should also be possible to say, I don't really like it, but I want to help you anyway. Or even, "Not bad, but maybe next time I will be the one who bites you". Or "I prefer to be the one doing the bitting". Offering options there shows preferences.
Then again, I think when it comes to kinks, people usually talk before trying things with new partners. If they can ask several times in the bear scene, they can to that is a kinky scene with Astarion. Depending the answers, you could know if Tav/DU likes it or not. Just saying.
I'm not into the new kisses and I would have liked new ones for spaw Astarion, but I think that if they wanted to add Tav as a sub, at least they should have done it in a way that people into that can enjoy it.
