As for the reveal - i think it’s about Viconia. She’s one of the most loved companions from prior games, she’s a drow and she’s a worshipper of Shar. Makes sense.
Isn't there's this thing about...
...her ending if she was romanced in Throne of Bhaal, where she is assassinated? Or am I misremembering things? I guess it could be retconned either way by resurrecting her since post-Spellplague a lot of dead characters were just brought back, and there could be a dialogue bit acknowledging the romance if the player wants it to be canon.
I wouldn't see this as anything more (or less) problematic than the fact that Jaheira or Minsc or indeed Viconia herself could have died in the course of either BG1 or BG2 depending on player actions. In fact, BG2 blithely ignored that they might have come to a sticky end or never have joined up in BG1. Personally, while I do like the idea of being able to preserve choices throughout a series, I can see how it can quickly become a nightmare for developers, if, eg, the fact that a minority of players might have romanced a companion in one game from 20 years ago means that she can't be used at all (or there needs to be an alternative character to play her role) in a new game. I certainly wouldn't blame Larian for sidestepping this issue and just picking versions of events that work for their story, though I hope they'll not be overly specific and rule out too many possible variations of the BG1/BG2 story, and I definitely hope they don't explicitly go with the Abdel Adrian version.
"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"