So unless I overlooked something, I think every past mega has been shown off now except (from least to most surprising):
- The Legends: Makes sense. The primals & Ray were probably never going to be here and the Lati were kinda iffy to begin with. Mewtwo I think is in but they probably don't want to show off before release. Diancie is in the same boat, though I won't rule being saved for the DLC. I could also our Hoenn folks be in the DLC too, considering Hoopa
- The Hoenn Starters: I did kind of think mega blaziken would be here, but I dunno. Could see the trio just being saved for DLC. But also, maybe ranked rewards? Guess it depends on if you can get any of them or not.
- Venusaur & Blastoise: Boy it would be real weird if these two weren't here, not even just considering Charizard but considering Lumiose is where you get the goofuses in XY to begin with. If they aren't traditionally available, probably Ranked rewards later down the line. Poor guys.
- Aerodactyl. This is THE one I most think I overlooked something, like maybe it was in a corner of a trailer or an image released or something. According to Serebii's pokemon list Aero is in the game, so I assume the mega is too. Would be a very arbitrary thing to leave out
- Glalie & Sharpedo: ???? I could have sworn I saw a Glalie or Carvanha running around but apparently not. What an oddball pairing. I have to assume these are in the base game because like really? All the other completely normal Pokemon but not these two?