I think he has a chance. Not a good one, but at least a better chance than he would if he were battling in any of the other game Leagues. The reason I say this is because this is going to be the inaugural Alola League, which gives the writers room for Ash's rank improvement even should he win this League since it will still be like an expansion League, rather than a well-known League like the Kanto or Johto Leagues. And, if game scenarios are included, there is also the Title Defense portion of this League so Ash could win the League, possibly even beating Kukui, but could lose to a future challenger, showing that he still has a ways to go even if he's won a regional League.