RE: What 'Mega' Pokemon formes are you hoping to see?
Mega Mantine is clearly the best idea.
Seriously though, I think that the Mega Pokemon are based off of Norse/Germanic Gods.
Blaziken -> Sultr (God of fire)
Lucario -> Forseti (God of Justice)
Amphy -> Thor
Mawile -> Loki (God of Deception)
Absol -> Fortuna (Goddess of Disaster)
Mewtwo > Magni (God of Power)
In addition, Xerneas and Yvetall are based on similar myths too, so I don't think it's too big of a stretch.
So I'll be listing other Norse Gods, alongside Pokemon I think can be them.
Metagross -> Odin (God of Knowledge, Metagross is smarter than a supercomputer)
Milotic -> Sjofn (God of Love. Milotic makes people calm. Could also be Delcatty)
Celebi -> Iounn (God of Youthfulness. Time travel keeps you young)
Chatot -> Bragi (God of Music. Makes sense huh?. Could be Kricketune or Wigglytuff though)
Cherrim -> Buri (God of Daytime. Cherrim blooms in sunlight)
Blissey -> Eir (God of Healing. Shouldn't need to explain this. Could be Miltank though)
Kangaskhan -> Frigg (Goddess of Motherhood. Yeah I don't need to explain this)
Gardevoir -> Hlin (Goddess of Protection. Gardevoir will sacrifice itself for it's trainer)
Lunatone -> Mani (God of the Moon. Hmmmmmmmmmmm)
Solrock -> Sol (God of the Sun. >_>)
Gyarados -> Ran (God of the Ocean (Magikarp is found in every body of water)
Ninetales -> Vali (God of Revenge. Red/Blue PokeDex calls it vengeful)