I feel like if we can use the Rotom Pokedex in battle it would possibly be a Psychic/Electric type. It would most likely be accessible in the post game because it would be too O.P. in the beginning of the game.
It would most likely get Psychic because Psystrike is Mewtwo's signature move.
The reason for Psychic instead of Steel is because a Steel type Rotom would be too obvious and most electronics have steel in them.
Psychic says that the Pokemon is smart and intelligent, also Rotom Pokedex would know over 721 Pokemon.
The Alola Region looks pretty awesome. The small Island in the middle looks almost like it would be the Alola League.(Possibly Battle Frontier?)
Looks like we will see some Ice types on the Island in the Bottom right.
Look at the very top of the map....Eyes? Looks like Hoopa eyes but seems like there is a secret legendary. There could be another trademark like Eclipse or something like that. Wait that must be the Eclipse Pokemon in the sky...
Alright the Characters. Hau looks like your rival (Obviously) and possibly gets the starter weak to yours.
Lillie could get the starter strong against yours.
Professor Kukui seems like he would act pretty chill. (I have a feeling there will be fan art XD.)
Hala looks like some old dude that is the old professor of Alola.
Legendary types. Solgalio's type is Steel/Psychic, Steel was seen on its body actually if you looked close on the Box art.( I thought it would be Poison/Psychic because the sun is made out of Gases.)
Lunala has a obvious type of Ghost/Psychic. Ghost has a dark feeling like the moon but fairy would have fit too.
Their signature moves are just in all awesome looking.
The Character designs are pretty awesome. Those bracelets they have on look familiar to Mega Bracelets but they have that diamond in them. Still mysterious...
It doesn't bother me if character customization is added, I just don't really care.
QR code scanner for the Pokedex could help me finally fill it out.
Man that was a lot of theory, opinion and speculation....