>>33029717It would up the stakes a bit too. It's no longer about being the very best in the region but being the best in all regions, in a symbolic manner. If GF are so dead set on including their story, it would at least give some more screen time to the PC.
The Looker side quest could also be included. Halfway through the Island Challenge, Looker and Anabel could show up and request your help as you are an up-and-coming new trainer with a lot of potential. The Ultra Beasts could be located in difficult to reach places and actually have an overworld model as well. The Aether Foundation agrees to help you capture/defeat but the ones you catch are sent to them for "study." Near the end of the Island Challenge, you travel towards the final Ultra Beast of the main game, Nihilego, but Lusamine gets there first without the player knowing. She captures it, merges with it, releases all the ones they had in captivity to wreak havoc, and hides out in Ultra Space. Any that you didn't capture can be explained away with a line like "Aether finished up the job after you left." Lillie could follow you around in the last Ultra Beast mission so she sees Lusamine, they have their little talk and conflict, Nebby gets hurt, then the two of you have to travel to Poni to get Nebby to evolve. More screen time for the player, and a bit for Lillie too.