Well, it looks like trials are back in, and gyms are going out the window. Loving the look of the trailer so far, and the fact that some of the trials have been changed, including some of the lesser known characters like Mina getting some trials. But that scene where Acerola's banging on the door of the Thrifty Megamart...you can already tell that these games are going to go down a dark path. Also, I had an inkling we'd get Tropius in Alola, cuz it looks pretty tropical on its own, and the way they showed off Mareep, Larvitar and Houndoom suggests that we'll get the event-exclusive mega stones through normal gameplay, or maybe just buy them from the tree.
There can also be some other stuff inferred from the trailer as well, for example the fact that one of Mantine's moves is the Gorebyss Spiral. This suggests Clamperl will end up in the new Alola dex.