IN fact, and I;ve been saying this for ages - I *fully* expect Viconia, what with Shar being so involved here.
I would actually be extremely disappointed if she didn't at least get a cameo somewhere in BG3. She fits this game better than any of the other characters who were in both previous games.
According to lore, she is hiding somewhere near the city with two drider servants.
She could easily be the leader of some underground Shar cult.
But although Viconia is selfish, arrogant and power-hungry, she is surprisingly not a person who seeks conflict.
If she is left alone, she is quite a peaceful person.