We no longer have gym battles so is it gonna be replaced by Z crystals?
Can we assume that Ash will only be getting the "main story" crystals and all the extra ones will be dummied out or given to other people?
Or will Kahuna battles be used as the new way to determine the pace? Given how they're only four of them I doubt it.
I think both the Totem Pokémon battles
and the Kahuna battles will count as our Gym battles this time around. I agree with U.N. Owen that Z-Crystals are probably going to be the badges of Alola. I think Ash will receive Z-Crystals not only from the Kahunas, but also from Trial Captains and/or some of the Totem Pokémon. With that said, I think both the Trials and the Grand Trials will determine the pacing of this series.
I assume Ash is going to get the Z-Crystals one earns by passing the Trials and Grand Trials (which may actually foreshadow the eventual type lineup of his team, but that's a discussion for another thread). He will probably also get Pikanium-Z (or Pikashunium-Z), Decidium-Z (if Rowlet fully evolves), and/or Incinium-Z (if he catches Litten and it fully evolves). As for the Z-Crystals that are
not earned through Trials or Grand Trials... Hopefully, the anime writers make Ash battle for those, or at least do something to genuinely earn them.
The only Z-Crystals I'm certain Ash will
not get are Eevium-Z, Aloraichium-Z, and the legendary Pokémon-exclusive Z-Crystals. Those Z-Crystals, and their corresponding Z-moves, will no doubt be shown off at some point (if not in the show proper, then in the movies), but I don't see Ash with an Eevee anytime soon (there aren't any new Eeveelutions this generation), and he sure ain't getting an Alolan Raichu.
I wonder how that Z-crystal could be introduced... Odds are it would be a previously undiscovered Z-crystal that Ash and Pikachu find, and one of the other characters give it the name, similar to Bonnie naming Ash-Greninja.
IIRC, Kiawe said that Z-moves are related to the bond between a Pokémon and its Trainer - specifically, the feelings of Pokémon and Trainer becoming one. If that's the case, then I can see Ash and Pikachu's strong bond giving rise to a new, never before seen Z-move. Or - and this is probably more likely, IMO - Tapu Koko or one of the other Tapus gifts Ash with the Pikashunium-Z
after it has deemed Ash as truly the Chosen One.