First thoughts:
The whole school thing, while happening, may not be what everyone is assuming. From the poster it basically says we'll meet Mallow, Lana, and Sophocles soon. Of course that can just mean we'll meet them in Corocoro soon, but I am interpreting it to mean that they, along with some others, (Lillie and Hau perhaps) will be part of an initial short school arc. To me this says that maybe the school we see in the background specializes (at least partially) in Z moves. Ash gets a Z bracelet right away. That says something.
Ash looks like he walked out of a One-Piece cartoon.
Second thoughts:
Based on my own deductions. I think that at the end of XYZ, when Ash returns to Kanto, we see him tired, but still looking for new challenges. Oak's cousin is in town, hears of his accomplishments, sees his bond with Pikachu, and invites him to Alola to attend (his?) school. When Ash gets to Alola he meets other classmates, as well as at least three of the trial captains. Maybe they are there to learn Z moves too or they are there to teach or present the island challenge to the class. Who knows? Maybe students who pass a certain level are allowed to challenge the Island challenge or go straight into a type of League. There are a lot ways this could go. With the later idea this could set us up with a few anime only rivals that show up later on for a type of league challenge. The possibilities are numerous.
The poster says clearly that Ash meets Tapu Koko right away. After that encounter, like the encounter of the main character in the Sun/Moon games, my bet is that he is invited to take part in the Trial Captain Challenge. Should he complete the challenge, he will "graduate" albeit in a less formal educational atmosphere. Maybe he will have to take a test at the end like all the other kids who learned things more traditionally.
It also seems that each of the Trial captains will be recurring characters if not a traveling group of 4 (which I don't think will happen). Mallow absolutely seems to be a traveling companion. Perhaps she is Ash's mentor of sorts, like a private tutor. If anyone needs a private tutor it would be Ash after all. The others, if they are not regulars, I can see appearing regularly, more so than the Kalos Trio. If it does turn out that the three Trial Captains are traveling with Ash, and are his official companions, then I could see all three acting as his tutor/mentor/friend/guide/etc. prepping him for graduation.
For now it also seems like Lillie could be a regular, if not a companion, with her very marketable vulpix.
I for one, while liking Mallow, hope that Lana also travels with Ash regularly because she has the water starter and I hate the way that thing looks and DO NOT want it with Ash. Ash with two or more regular female companions is cool with me.
It seems rather clear that Ash gets at least the Grass Owl. I'm down with that. I'd rather him not get all three. Rockruff and his daytime evolution would be awesome too, though but I'm not getting my hopes up.
And finally: Where the heck is Hau?
