. . .In that case, I suppose whether it counts as a new Generation proper or not depends on whether or not Game Freak hit writer's block in terms of new mechanics. IMO the last two generations have had more superficial mechanics changes than the ones before them, so it could go either way in my mind whether they would bother introducing new ones alongside the next region. If they do, I suppose they could go the route of how that one fan Tweet-rumor brought up the concept of Pokémon Fusion that has been tossed around forever.
Unless mechanics changes are referring to the new Battle Types, in which case we've gotten three in the past two Generations and I guess I could see us getting another. I just remembered how much I want Triple, Rotation, and Inverse battles to stop being neglected and shoved off onto out-of-the-way NPCs instead of peppering them in like Double Battles, though. We don't need them to get entire Gym Leaders like Lisa and Tate, but I kinda wish they felt less. . .tacked on.