Here is, objectively, the best changes USUM could possibly give us.
Strap yourselves in boys.

>Gym battles brought back
Now hold on my little cuties, because I don't want gyms to straight up replace Trials, I want them to coexist together. Obviously Trials will go away after we leave Alola, but they're something that makes Alola unique, and I have no issue with them, my issue is that they replaced gyms with trials rather than have both. Why not have both?

See here's the thing. Gyms could simply serve the same role gyms have always served, and that is getting badges so you can enter the pokemon league and face the elite 4 to become champion.
Trials can simply be used to get you Z stones. What's wrong with that? That's much better than just finding them in random caves. You have to face a boss Pokemon of sorts to get them.

So what about the Island Kahunas then? Well why not have them stick around too? Their purpose simply being that they must be defeated in order to move on to the next island. Pretty simple, really.
This type of gating seems flawless to me and I can't see a SINGLE reason as to why this would be an issue for anybody, or a negative in any way for that matter.

>A fifth island
Will this happen? Who knows, but what I do know is that the game would benefit greatly from it. My issue with Alola is that it feels quite small. I'd like one more island that serves as a post game haven, as for what that post game stuff could entail, well you'll just have to let your imagination run wild, but first things first, we need more space to play and a fifth island solves that the best IMO.

>More new Pokemon in general.
Last but not least. New Pokemon period, new Alolan forms, new UBs, whatever, I want them all.
Naturally I hope we get some non gen 1 Alolan forms but at this point I'll take anything. Still waiting on my Alolan Victreebel after all.

That's all USUM needs. That is the winning formula. Pokemon following you is a bonus but not necessary in my eyes.