If Mega Evolution is in. I think it goes without question that most of the Mega Evolutions that are present in the Platinum Dex will be obtainable, but I've got two questions:
1. Where would the several Mega Stones be obtained (or will some be gate-keeped until PostGame (such as Mega Garchomp for example).
2. Would you like to see new Mega Evolutions (if answered, please add an answer to question 1 as well.
Here's a list of pokémon capable of Mega Evolution from the Platinum pokédex, per generation (they're quite evenly distributed 4-6 per generation).
Gen1: Alakazam, Gengar, Gyarados. Speculation being that the Kanto Starters will also be included.
Gen2: Scizor, Heracross, Houndoom, Steelix.
Gen3: Medicham, Gardevoir, Altaria, Glalie, Absol.
Gen4: Lopunny, Garchomp, Lucario, Abomasnow, Gallade.
My takes on question 1:
Gen1:
- Alakazam: Mira after subquest.
- Gengar: Fantina during PostGame.
- Gyarados: Wake during PostGame.
- KantoStarters: Depends on whether or not they're in or not, but I'd expect a Sycamore/Oak cameo ala XY.
Gen2:
- Scizor: Aaron during PostGame.
- Heracross: FloaromaMeadow NPC during PostGame, possibly Barry.
- Houndoom: Flint during PostGame.
- Steelix: Byron during PostGame.
Gen3:
- Medicham: Maylene during PostGame.
- Gardevoir: Lucian during PostGame.
- Altaria: Cynthia's Grandma at Celestic Town during PostGame. Dragon/Fairy is too broken for maingame storypurposes.
- Glalie: Candice during PostGame.
- Absol: There's no NPC's on the top of MountCoronet.. So I don't have a clue, but I guess something could be done about it.
Gen4:
- Lopunny: Cheryl after subquest.
- Lucario: Riley after subquest.
- Abomasnow: Buck after subquest. Buck would get introduced earlier in the game and wants to explore Snowpoint Temple.
- Gallade: Marley after subquest. Marley would get introduced earlier in the game and wants to
- Garchomp: Cynthia during PostGame.
Basically I'd like the Sinnoh Mega's to be available early in the game and the rest be PostGame. I wanted to give the 'stat'-trainers a bit more to do, so I lumped the Mega Stones onto them. Lopunny+Cheryl is because of Eterna Forest, Riley should be obvious, Buck is the 'Def'-trainer, so bulky Abomasnow works and Marley is the Speed-trainer, so Gallade for her. Mira is the Special Attack-trainer and Alakazam is her ace. It's not a Gen4 pokémon but it would feel weird to give all other Stat-trainers a quest and not Mira. Could also give the Gardevoirite or the Gengarite, but I think I already gave those to suitable characters to distribute already. That's to say if they get distributed by characters all together, they might as well end up in a BattleTower shop for BP for purchase.
Still, I'd really want to use a Mega Lopunny during a playthrough. I don't mind if I only get to use it for two/three gyms, but having that option to make an otherwise pitiful pokémon viable against E4-members would be awesome.