So uhm, Cydonia published a video commenting on a gameplay they got to watch.
It's in Italian (but I expect more in other languages to pop out eventually), but he says that Isle of Armor has a "scaling" system similar to the Wild Area, but also applied to actual trainers. They say they don't know if this scales all the way to level 100.
He also says there's plenty of dungeoning and actually hidden areas to explore. (that however were not shown), however in general we're looking still at linear areas combined with extra optional paths.
Also, according to him, GameFreaks said that this DLC should have "some of the hardest challenges yet to come".
(Also, they improved the trees. Very important details :P )
Edit: Oh, yes, he says that you get an additional Exp share that can be assigned to a single pokemon and makes it get even more experience.
Edit2: I see Serebii is covering this as well, so yes probably some more vids in English should appear shortly enough.