I don't know what you are taking about here. Kukui hinting that there would be a League = flat out indication by the writers that there would be a League in which Ash will participate. There was absolutely no point in hinting that Kukui would build a League if Ash didn't participate in it, because then the League won't be shown at all. This is the Pokemon anime, it follows the journey of Ash and Pikachu. If Ash doesn't compete in the Alola League, then the League won't be shown in the anime at all, and there's literally no point for the writers to have Kukui build a League if the League isn't shown at all. In all of the Leagues shown so far in the anime, Ash's battles have been the main focus, and how far Ash makes in the League. Once Ash is eliminated from the League, the remaining battles in the Leagues aren't shown anymore/just skipped over, like what happened in the Kanto, Johto, Hoenn, Sinnoh and Unova Leagues. There is literally no point in the writers having Kukui build a League, plus teasing/hinting and then confirming that Kukui will build a League not once, but twice, if the writers don't want to show the League in the anime. Why would the writers bother doing all this if they don't even show the League in the anime, which will happen if Ash doesn't compete in it. Makes no sense at all.
The chances of there not being a League/a League being built with Ash not participating in it is pretty much 0%, given what has been indicated in the anime so far.
And you're still ignoring the fact that Kukui was inspired to build a League when the heard of the Kanto Gyms and League, and he further finalized his decision when he heard of Ilima participating in the Kalos League. When he's building the League being inspired by 2 standard Leagues which both have a tournament like format, it's very unlikely/hardly makes any sense that he'll build the League in any different format than those 2 Leagues, something other than a tournament like the Orange League. What you're implying with the League being like the Orange League is that Kukui will solely build the League for Ash, when he completes all the Grand Trials, to have a one off match with Ash for the Champion title, which sounds ridiculous considering he has been inspired by 2 standard Leagues which have a tournament like format, to build the Alola League. And saying that 'I doubt that there will be enough challengers who would complete all four Grand Trials to compete in the League' is a ridiculous arguement to use, because by that logic one can also say that 'I doubt that there would be enough challengers who would complete earning all 8 badges to compete in the League', in cases of standard Leagues.