For me itās Svanrige, the could-have-been King of the Isles, who sacrificed his own mother and honor for the sake of what was right. Crach says Svanrigeās options are death or exile, so it would be awesome if he appeared again as a wandering mercenary in a distant land for Ciri to meet.
This is of course only the case in the Cerys ruler path, as in the other paths his motherās crimes are not found out, or he becomes King himself and a great one at that.
But since I imagine that Cerys is the most popular choice for ruler, I wouldnāt mind it being the canon path, or an option to choose it at the start like what was done with Letho.
As for other characters I wouldnāt mind to see, who are truly obscure, I wouldnāt mind seeing the blood and wine Manticore Witcher who gave up the trade to become a wandering priest of Lebioda.
āJeromeā could also be someone to meet, also from blood and wine he was the Griffen Witcher involved in the Mutagen experiments. It was implied he died, but no body was in the cave where his last notes are found. Who knows, maybe if they want to bring the mutagen system back for Ciri, using Jerome to share the secrets could be a lore friendly way to do it.