In Pokémon Sun/Moon, since you're the first Pokémon League champion, you're set to defend your title as Pokémon League Champion, rather than repeatedly taking the title from your rival or whoever the champion before you was. Unlike previous iterations in the series, who you fight in the championship match changes.
So far, after beating
I've had to defend my title against
Hau and Molayne.
This leads me to believe that there are a vast number of challengers I could have to defend my title against. However, at least one captain is also a member of the Elite Four, so not all captains could be challengers. That said, is there a list of who all could potentially challenge me? I know Red and Blue are in this game, so could they challenge me?