Speaking personally, a hugely masochistic side of me would like for there to be a game where all three gimmicks exist simultaneously just to see what kind of mess that would create. That said, if that ever does happen chances are that at least Dynamax/Gigantamax is going to need to be nerfed a little, because as things are now I feel like it's by far the most overpowered of the three and would probably beat the other two nine times out of ten. Z-Moves especially (or at least the purely offensive ones) look downright obsolete next to Max Moves.
I'll be honest, I do greatly miss both Megas and Z-Moves, and while I think it's unlikely at best, I do want to see them both make a return in BDSP, even if it's just in the postgame.
That game would be Pokemon Masters EX