An example of this is in the OP; only water and flying types will be allowed, just like how Primal Groudon can only have ground-type followers and MMX (used to) only have psychic type followers. Flying type followers would still be able to follow the Mega Gyarados, but that still leaves the question of why you would want to.I pondered this, but how will type changing Gods affect teambuilding?
Take example one wants to run Gyarados w/ Gyaradosite as the god. Do you run flying type followers or dark? What happens if the Gyarados mega evolves, will all flying type followers become obsolete? If dark types are following said Gyarados, what happens if it dies before mega evolving? Honestly its really confusing and I'd like it to be addressed.