The Dragon Lord
I hope that the volcano on the starting island is accessible later on. It could serve as a nice post game challenge.
On an unrelated note, I found something interesting while I was looking at the map of the Alola region.
View attachment 15636
It looks like it says the word "Delta". This seems extremely odd and doesn't seem like it should be there. It could relate to the Delta Emerald trademark, but I could also be reading way too far into this. I hadn't seen this anywhere else, so I'm pretty sure that this is a new find.
No matter how hard I squint, I'm just not seeing it. You're probably just looking too deep into it.