Some of them are extremely unlikely though. I can't see Ash with Rapidash, Houndoom (Its a hellhound, which i doubt they will ever give Ash), Blaziken (Is a starter and the main mon of a travelling companion - unlike Dragonite, who came post-league and the main mons were Axew and Excadrill anyways, i doubt Ash gets mons that are heavily associated with companions or are their signature Pokemon). Considering the mystical status surrounding Volcarona, i doubt Ash is getting that one as well - at least in this series, because he has Lucario.
Realistically, the only Fire type Ash can have are Arcanine, Ninetales, Magmortar, Chandelure, Pyroar and the gen 8 fire types (Of which Centiskorch is extremely unlikely, so that only leaves Coalossal).