So far, the new mega evolutions revealed with ORAS all hold a pattern: there's a logical reason why these Pokémon would be picked. No "man, this is such a random choice" so far. Sceptile and Swampert because they're starters and Blaziken already has one, Sableye because it's Mawile's counterpart, and the latter already has one, Kyogre and Groudon because they're the cover Pokémon, and Diancie because it's an upcoming event and Gamefreak must've realized how crappy they made it.
So, what else do you think will get the mega treatment? There's been a lot of hype over Sharpedo and Camerupt since Maxie and Archie have mega triggers of their own, and it means one of two things: either it's for their respective aces, or it's for Kyogre and Groudon. I wouldn't mind Sharpedo and Camerupt getting a hand, because they really, really need it. Something else I want to see is Mega Milotic, which is in my opinion one of the most likely introductions, because while it's not a version exclusive, it's still clearly Gyarados' counterpart, and it's a kickass Pokémon that also is in dire need of help. I remember being so disappointed when it turned out its typing wasn't changed to Water/Fairy, so there might be a second chance here. Don't screw this up, Gamefreak.
But the one thing I want the most is for Gamefreak NOT to get scared by the prospect of giving huge boosts to weaker Pokémon. While anyone with a brain could've told you Blaziken, Lucario and Gengar would end badly (although credit needs to be given for realizing base Lucario was going to fall into obscurity), before the game came out no one would've imagined Kangaskhan would've wrecked as much face as it did, in major part thanks to the exalted presence of Power-Up Punch. Now I've been told Gamefreak actually acknowledged that they went overboard with it (though I think just preventing the baby from triggering added effects might be all that's needed to balance it), though I have yet to see that for myself, but I don't want to see a whole bunch of megas underperform just because Gamefreak held back to avoid another Kangaskhan fiasco. We've already seen it happen with Mega Sableye. Now think of all those Pokémon that were handed god-tier destruction tools, such as Charizard and Mawile, and STILL aren't gamebreaking. We need more of that kind of improvement to salvage bad Pokémon, and I hope Gamefreak considers the solid hits more than the one miss nobody saw coming.
Edit: Mega Metagross confirmed! Not a huge surprise, being Steven's ace and all, but one can only wonder how Mega Charizard X is involved in all of this. Anyway, here's to hoping for a nice ability. How about Defiant? That'd be great...
Also, a Hoenn Dex expansion has been confirmed. I think everyone saw it coming, considering the Kalos Dex had a massive 450 Pokémon, so going back to 200 would be really lame. Can we hope for better E4 lineups? The originals were littered with duplicates and NFEs, and made for the worst League challenge in my honest opinion.