And one more advantage, which I hope to see in this generation: As proven by Charizard and Mewtwo, there's the possibility of multiple Megas for a Pokémon. That potential is quite underused at the moment, but I believe we will see more of it in later generations. If Game Freak ever makes an unbalanced or poor Mega, they aren't bound to the conventions of traditional evolution. They can just introduce another Mega Stone for the same Pokémon, giving it another chance. Moreover, it allows them to drag a Pokémon into the spotlight several times across several generations. Giving, say, Mawile an evolution would have been a one-off trick. Giving it a Mega suddenly made it very relevant. They could easily do that again by giving it another Mega. Plus it also gives a player several more options for what to do with his favourite Pokémon. I can easily see Game Freak revisit some Pokémon for another round of Megas in the future.