Parmandur
Book-Friend
I mean, they could do a serious D&D All-Stars thing here, if they are going for it.Nezram
Nezram's big thing is Planeswalking, and its only rescently he even returned to Toril, to help rebuild Mulhorand and liberate it from the Imaskari.
Tasha is a possiblity.
Drizzt is odd, but possible even recent events.
Fizban. Its not an accident that he was in a UA that otherwise was FR lore.
Vee from Eberron
I don't think Think there will be any Planeswalkers aside from Vee who aren't from either Toril, Oerth, or Krynn.