[quote=@SleepingSilence]
The question is "who are they going to replace him/the other cast with?" (Pretending they haven't already shown the generic anime boy/girl self-inserts.)[/quote]

I presume they already revealed that with the two new characters. One has a special pokeball and the other has something to do with a pendant/necklace thing. There's a fan theory out there that the girl is probably Ash's daughter or at the very least a fan of his (given the green arrow/check mark hair piece the girl has), but we don't really have much more information about the new anime yet so who knows.