You want proof that Game Freak doesn't give a shit about buffing underwhelming mons using Mega Evolution? They gave Mewtwo - who, btw, is a manmade Pokemon created over a thousand years after Mega Evolution was first discovered - two Mega Stones. Both of which also predate their potential recipient by at least a millennium. Just let that sink in.
On a more serious note: I guess while we're talking about Mega Evolution, I'll say this: Mega Evolution should stay in gens 6/7.
First off, I think keeping it there helps X/Y maintain what little reason there may be to replay them, and adding them to SwSh or anything released after - especially during the main adventure - would essentially render X/Y completely obsolete (if ORAS don't already, of course).
Secondly, don't get me started on what kind of nightmare online battling would be if things like Mega Mawile and Mega Salamence could both Mega and Dynamax simultaneously.
Third, I know enough about this franchise's fanbase to say with a modicum of confidence that there's just no way to bring Mega Evolution back in a way that satisfies enough of them. If GF just brings back the same Megas as before, they'll complain about the lack of new ones. If they do introduce new ones, they'll complain about how one certain Pokemon or another didn't get one. If such a mon does get one, they'll complain about how its design ruins it, or how it didn't get buffed enough, or whatever else. I can't see a winning formula for reintroducing Megas that doesn't piss off a sizeable chunk of the fanbase, so I think it's best to just avoid activating the shitstorm altogether.
Lastly, I don't think the most common argument I hear in favor of bringing it back - that being its ability to buff underwhelming mons - holds much weight, all things considered. There are other ways to do that without giving such a thing a Mega (e.g. the various toys Pelipper got in Gen 7). Plus, looking at the distribution of Megas we currently have, I don't find most of the recipients to be all that underwhelming in the first place (not being a top-tier threat in OU doesn't necessarily count as "underwhelming" to me), and frankly, I'd bet more money on Game Freak creating 3 more Mega Mewtwos than I would on them creating a single Mega Ledian or Chimecho.
Considering all of that, I think it's better for all parties involved to just leave Mega Evolution in the past. And before you ask, yes, I also think Z-Moves and Dynamax should stay in gens 7 and 8 respectively.
On a more serious note: I guess while we're talking about Mega Evolution, I'll say this: Mega Evolution should stay in gens 6/7.
First off, I think keeping it there helps X/Y maintain what little reason there may be to replay them, and adding them to SwSh or anything released after - especially during the main adventure - would essentially render X/Y completely obsolete (if ORAS don't already, of course).
Secondly, don't get me started on what kind of nightmare online battling would be if things like Mega Mawile and Mega Salamence could both Mega and Dynamax simultaneously.
Third, I know enough about this franchise's fanbase to say with a modicum of confidence that there's just no way to bring Mega Evolution back in a way that satisfies enough of them. If GF just brings back the same Megas as before, they'll complain about the lack of new ones. If they do introduce new ones, they'll complain about how one certain Pokemon or another didn't get one. If such a mon does get one, they'll complain about how its design ruins it, or how it didn't get buffed enough, or whatever else. I can't see a winning formula for reintroducing Megas that doesn't piss off a sizeable chunk of the fanbase, so I think it's best to just avoid activating the shitstorm altogether.
Lastly, I don't think the most common argument I hear in favor of bringing it back - that being its ability to buff underwhelming mons - holds much weight, all things considered. There are other ways to do that without giving such a thing a Mega (e.g. the various toys Pelipper got in Gen 7). Plus, looking at the distribution of Megas we currently have, I don't find most of the recipients to be all that underwhelming in the first place (not being a top-tier threat in OU doesn't necessarily count as "underwhelming" to me), and frankly, I'd bet more money on Game Freak creating 3 more Mega Mewtwos than I would on them creating a single Mega Ledian or Chimecho.
Considering all of that, I think it's better for all parties involved to just leave Mega Evolution in the past. And before you ask, yes, I also think Z-Moves and Dynamax should stay in gens 7 and 8 respectively.