Pokémon Z: How Would You Have Done It?
Viola: Scolipede, Crustle, Durant, Heracross, Vivillon, Mega Beedrill
So, this one's actually a little tricky, since Vivillon is the only Bug-type Pokémon introduced in Gen 6. I feel like my hand is a bit forced here because although you certainly could give it a Mega Evolution, maybe with all sorts of colorful pixel patterns that combine the existing ones, I just don't think it would be... all that... good? And I quite like Mega Beedrill, and it still fits the convention of "early forest Bug." Anyway, here I tried to stick to bugs that seemed a little more naturalistic; ones that Viola might photograph in their natural habitats and would maybe make for good artistic motifs.
Grant: Golem, Tyranitar, Aurorus, Tyrantrum, Mega Aerodactyl and/or (Mega) Rhyperior
Golem and Tyranitar are really rocky designs with strong ties to mountains. Same for Rhyperior, which is my consideration for Grant's new Mega. I'm picturing something that really cranks its bulkiness up to eleven, with lots of jagged rocks jutting out where the orange plating is, and with the two arm cannons swelling to such a size that it has the silhouette of a mountain range. But if I had to stick to established Megas, I'd go with Aerodactyl (while still keeping Rhyperior on the team), since it's a fossil like his Aurorus and Tyrantrum, and would be helpful for a mountain climber in emergencies.
Korrina: Machamp, Hawlucha, Mienshao, Hitmontop, Poliwrath, Mega Lucario
Her existing team Gym team, plus Mega Lucario, which I think is pretty much a given even if we consider the possibility of new Megas. Added Hitmontop (all that spinning and balancing matches with her roller skating) and Poliwrath because, well, because. She lives on a coast?
Ramos: Jumpluff, Victreebel, Leafeon, Roserade, Mega Venusaur and/or (Mega) Gogoat
Existing team plus two garden-ey additions. If we get a new Mega, I'd say Gogoat's the obvious choice (huge horns! tree branches sprouting off of them! even thicker leaf coat!) but if not, Venusaur fits by dint of being covered in flowers.
Clemont: Emolga, Magnezone, Electrode, Lanturn, Mega Ampharos and/or (Mega) Heliolisk
Electrode added because it kinda fits his Gym's quiz theme (every time you find a Poké Ball on the ground, there's a chance it could be Electrode), Lanturn and Ampharos added because of how they emit light, and he's the leader/designer of Prism Tower in the Pokémon world's equivalent of the city of light. idk what a Mega Heliolisk would look like.
Valerie: Mr. Mime, Sylveon, Togekiss, Wigglytuff, Mega Mawile and/or (Mega) Granbull
Gonna go ahead and say giving Sylveon a Mega feels too weird to me, so I'll either have her Mega Evolve her Mawile or I'll give it to Granbull, a Johtonian Pokémon since Valerie comes from there. I feel like a Mega design for Granbull could do a fun thing and actually make it more cute. Bows and frills and the like. Added Togekiss and Wigglytuff because they seemed on-brand.
Olympia: Sigilyph, Slowking, Meowstic, Gothitelle, Mega Alakazam and/or (Mega) Malamar
Similar to Sylveon, it feels a little weird to me to give Meowstic a Mega. So I'd give one to Malamar instead, or just give her good ol' Alakazam. Alakazam and Gothitelle can both see the future which Olympia can also do.
Wulfric: Cryogonal, Beartic, Mamoswine, Cloyster, Mega Abomasnow and/or (Mega) Avalugg
Bottom line is I added bulky Ice-types. If you can't see why this guy should have a Beartic then I can't help you.
Malva: Pyroar, Heatmor, Flareon, Chandelure, Mega Houndoom/Talonflame
Swapped Torkoal for Flareon. Add Houndoom (she's eeeeevil) and Heatmor (Team Flare has a very Social Darwinist bent so consider the Heatmor/Durant relationship). Consider giving Talonflame a Mega (and presumably busting the metagame even further in the process), but if not, Mega Houndoom would be okay.
Siebold: Clawitzer, Gyarados, Kingdra, Whiscash, Mega Slowbro and/or (Mega) Barbaracle
Add Kingdra and Whiscash to his team. I would give Barbaracle a Mega Evolution, but Slowbro would be fine too - Slowpoke is in the Kalos Dex, and Mega Slowbro didn't get much of a spotlight in ORAS. If we went that way, then I'd replace his Starmie with it.
Wikstrom: Klefki, Scizor, Escavalier, Mega Steelix/Aggron/Aegislash
Probopass is swapped for Aggron. Added Escavalier (how was this not there to begin with?) and Steelix. Aggron or Steelix could then be his Mega (of the two, I'd prefer Aggron since it's very much like a bulky suit of armor), but if we're inventing new ones, then I say go all-out and give Aegislash some crazy new design. A full set of knight's armor maybe? Or a big sword wielding a shield and another sword, to fold back into Doublade's concept?
Drasna: Dragalge, Druddigon, Altaria, Mega Garchomp/Goodra/Noivern
Added Garchomp since she's from Sinnoh. Goodra can come too since I'll be taking it off Diantha's team. She can either Mega Evolve the Garchomp or we give one to Noivern or Goodra, either'd be fine with me.
Diantha: Dragonite, Amoonguss, Lucario, Zoroark, (some form of) Rotom, Mega Gardevoir
I picked Dragonite and Lucario because they're popular, and in particular, I think Dragonite suits Diantha's soft design. Amoonguss, Zoroark, and Rotom are chosen because they are all Pokémon that I think could be said to suit her status as an actor. Amoonguss is a method actor (pretending to be a Poké Ball), Zoroark disguises itself as a different team member (it's an understudy), and Rotom is a versatile jack-of-all-trades (and also brushes on the idea of using props). Additionally, Lucario and Zoroark are actual movie stars! Dragonite I would say also has had a memorable scene in M01.
A note on Lysandre - Because Mewtwo was so prominently featured in XY's prerelease material, I figured it would end up having some role in the plot, but alas, it was just a post-game extra with no explanation whatsoever for the existence of its Mega Stones. For a long time, I've thought that maybe Team Flare should have been responsible for the creation of its Mega Stones, with Lysandre using one on his team. This made sense to me in the context of X & Y - in X he would presumably use Mewtwo X, which Xerneas hits supereffectively, and in Y he would use Mewtwo Y which Yveltal can take care of, so it's a little more manageable and more of a reason to use the mascot on your team for that battle. This obviously wouldn't work out in my plot revision up above, but I still can't shake the feeling that it might be good. After all, it's a little odd, I think, for Lysandre to have captured Xerneas/Yveltal and to then use them in a battle against you (which necessarily would mean knocking them out), only to then still be able to use their power in a way that draws Zygarde's attention. So maybe if Xerneas/Yveltal spend the whole climax trapped and Lysandre uses a Mega Mewtwo instead?