When PWT was revealed they've used Brock and Misty (among others) to promote the feature

Now Brock and Misty are back in the anime and the games show us Lt Surge's gym replica

I doubt PWT will happen in USUM (afterall Red and Blue are already Tree bosses and Tree's gimmick are few old characters) but i think all Kanto gym leaders will appear in USUM

Kukui in the past traveled through Kanto and battled the gyms. He probably invited them all to Alola and we'll have them as extra cameos and more characters to the Battle Tree

Thoughts?