Nefermandias
Hero
Dalamar appears in Shadow of the Dragon Queen.My guess is that they'll mostly be Archmages that have already appeared in 5e. Mordenkainen was in Curse of Strahd and Descent into Avernus and Tasha was in the The Wild Beyond the Witchlight, so those are my guesses. I don't think Elminster has appeared in any 5e books yet, but he is big enough of a character that he'll probably be included.
My guess is Mordenkainen, Tasha, and Elminster.