I posted this elsewhere a while ago, but while we hold out for the new Corocoro, here are my thoughts on the upcoming ORAS megas
We got 30 Mega-Evolutions for Pokemon X and Y - including the X and Y forms + Mega Lati@s. Perhaps another 20 coming? We've got 10 so far (or 12 if you include the Primal forms). 30 is too much for ORAS tbh. 20 would be reasonable.
E.g.
1. Slowbro
2. Miltank / Kingdra / Blissey

3. Sceptile
4. Swampert
5. Slaking
6. Sableye
7. Sharpedo
8. Camerupt
9. Flygon
10. Altaria
11. Milotic
12. Salamence
13. Metagross
14. Kyogre
15. Groudon
16. Rayquaza
17. Mightyena / Linoone / Roserade / Dusknoir / Tropius

18. Lopunny
19. Audino
20. Diancie
Basically, my reasoning is that they're all gonna be gen 3, except for one of each other gen (Slowbro, Lopunny, Audino and Diancie confirmed, which leaves one gen 2 mega #Pray4Kingdra ). Also in the Slowbro trailer, every Pokemon except Slaking had a mega, so I assume Slaking will have one. The rest is guesswork.