Here's a few things you should look for.

New pokemon:
Musquito pokemon is real
Flying/Fighting is real
Almost a dozen new baby pokemon, possibly all from Johto pokemon.
No New evolutions confirmed (could still change)
No mega evolutions
No new pokemon forms
New dog based pokemon Normal type
New Bird pokemon, evolves into Flying/Steel
Legendary pokemon:
both Dragon/Steel Type (Sword like Tail and Daggers on hands, Shields on Hands and back).

New introduction (BIG SPOILER):
Pokemon combo:
You can combine 2 pokemon in your party (will not always be particular combinations, not everything you want either.
ex. Deoxys&Psychic Type Pokemon works, 2 Electric Type pokemon doesn't) make a new ''pokemon combo'' move.

Some specific sets:
Eevee&Pikachu
Gallade&Guardevoir
Solrock&Lunatone
Magikarp&Feebas
POSSIBLE Legendary combos:
Regigigas&another regi
Ho-oh&Lugia
New Legendaries

Legendaries can combo with non-legendary pokemon for non specific combo moves (Very similair to Z-moves, where there are moves for each type and specific moves for some pokemon).

Pokemon combos can happen once per battle, either damaging or a huge boost stat (Full Eclipse, Super Splash, Hyper Bolt)
The moves are the same type as the type the pokemon share. If types aren't shared it stays as one of the types (no consistant way of telling which one).
Can't use pokemon combo until you are halfway through the game (Similar to OR/AS)

Professor Spruce is real, female professor.
Is a big baby pokemon fanatic.
Baby pokemon are a big deal.
Hatching rewards!