The problem with gens after 4 is that everything new that they add to the game play is removed in the next gen, 5 introduced triple battle which where removed in gen 7 and barely used in gen 6, gen 6 introduced megas and by gen 7 they didn't even introduced new megas, gen 7 introduced Z-Moves and if the rumors about armored Pokemon are true (lets's hope not) they will throw Z-Moves for armored Pokemon in gen 8.
All those upgrades could easily all put together, i will give you triple battles because it seems it has to do with the N3DS not being able to handle triple battles, but Megas and Z-Moves don't have excuses to be removed except for game Game Freak being lazy and don't caring anymore.
