Do we know for a fact that Mega Evolutions even get counted in the Pokedex? Because they don't stay Mega after a battle is over, so technically they shouldn't even be listed in the regular Pokedex (Maybe in a sub "Mega-dex" though)
So there's still a decent chance I would say for more evolutions of old Pokemon to be in game.
Well that's just speculation. And correct me if I'm wrong but I don't believe gen 5 introduced new evos for old pokemon. Maybe it's their new way of toning down the number of pokemon? idk.
It didn't, but Pokemon gens go like this:
Gen 1: New Pokemon (obviously)\ Gen 2: New Pokemon + lots of evolutions for old Pokemon Gen 3: New Pokemon (almost no additions to older Pokemon) Gen 4: New Pokemon + lots of evolutions for old Pokemon Gen 5: New Pokemon (almost no additions to older Pokemon)
So Gen 6 was expected to be the "tweak old Pokemon" generation. And in many ways it is (Mega Evolutions for tons of Kanto Pokemon), just not in a Pokedex-bloating way.