With the Rite of Island Challenge ultimately replacing gym battles for Pokémon Sun & Moon, I've been playing around with new ideas for the trainer cards in order to come up with a replacement for gym battles. This was a beta design I thought of based on my own theory of how the trials are going to work in the game.
Rather than receiving gym badges, I believe that you will receive a Z Crystal after completing each trial, thereby allowing you to unlock one of the generic Z moves such as Gigavolt Havoc or Bloom Doom. As such, there could be one trial and Z Crystal for each pokémon type.
Granted, this is just one theory and I may be proven wrong once the games are released, but I've been thinking of ways to modify the trainer cards for Sun & Moon.