Because I am a big fan of type-match ups, i would very much like Krokorok to be caught before the electric gym and be used in there, but I highly doubt that would happen.
IMO, pikachu/scraggy will take on the electric gym.
Snivy/Oshawott or their evo forms will take on the ground gym. Though scrafty/pignite could also turn out to be the star by taking out excadrill.
Pikachu/Unzefant will rule the flying gym.
Scrafty and Pignite/their evolutions will take on the ice gym.
All three starters at whatever form they will be at that point will take on the dragon gym. Pikachu might sit this one out.