i will talk about classes which make sense in X expansion that suit the idea , for example we are bfa and lets say there is big possibility we will get old god expansion so here is my guess , also remember missing classes from lore is limited
1- necromancer will come in (Bolvar Fordragon/undead ) expansion
2- warden will come in ( legion return / demon expansion in far future )
3- tinker is little bit complicated to think for expansion for them but they will come anyway sooner or later since they are big part of lore, and we saw Gelbin Mekkatorque in legion trailer and we also so goblin and gnomes mining azerite and creating booms but still i believe chance see them sooner is low since its tinker have nothing to do with old gods
4-blade master , the samurai orcs but again like tinker not sure it or how it will make sense in next expansion
5- spell breaker , in case you forget about them its these guys in sunwell guard with glave and sheild .they got some stuffs happen in sunwell but again i doubt there is strong enough reason to join next expansion after bfa
6-i believe next class will be ( shadow hunter ) why though ? first of all trolls/zandalari have very strong connection in their lore/storyline about old gods and ghoon , also in legion the loa make sylvanas warchief and Vol'jin coming back in bfa too and probably will play big role in next expansion after bfa , shadow hunter is trolls and have strong connection with the loa and most big factor is (((((((((((((((((((( we don't have hunter-like class with throwing stuffs )))))))))))))) shadow hunter can have 1 spec with throwing spears and 1 magic/another ranged spec , and 1 healing witch doctor spec which lore wise it make sense for this class to be the next after bfa
tell me what you guys think ?
PS: sorry english not my main language