Well, clearly they said not all pokemon can mega evolve. Right now, i'm thinking of which Sinnoh forms of Johto, Kanto, and Hoenn pokemon can mega evolve. I know that XY did not introduce megas for advanced pokemon like some Sinnoh, Unova, and Kalos. Now that ORAS is introducing Unova megas. Lets talk about which pokemon like Togekiss will get mega evolutions.
First, Gallade is the most likely. Mawile got a mega in XY, Sableye in ORAS, now Gallade looks to complete the set.
Next, I can see Porygon-Z getting one as well. It stands out the most.
Picking one from Johto is tricky, theres lots of good ones like Gliscor, Togekiss, Weavile, and Mamoswine. Anyone got an idea?