@DummyZ -
I'm pretty sure that they will be introducing new mega evolutions, actually.
It wouldn't be fair if Blaziken is the only Hoenn starter with a mega evolution, as this would extremely disadvantage the other two Hoenn starters.
Also, there are mega evolutions for Latios and Latias, which most likely won't be available normally in X or Y, but rather in Omega Ruby and Alpha Sapphire, thus furthering the possibility of new mega evolutions.
Also, it wouldn't be a wise choice for them to not introduce more mega evolutions, as they are kind of the gimmick for Gen. VI, along with 3D graphics, of course.
In my book, just because one starter got them, doesn't necesarilly mean that the others need them. By that logic, Mew and Gallade should've gotten Megas as well considering they both share relationships with other Pokemon who got Megas. There could've always been a reason why only Blaziken got one (fan-favorite, maybe?). In any case, Mega Swampert and Sceptile would've been in X/Y's coding, just like Mega Latios and Latias were.
Being of course speculation, Megas in the new games are still possible, but I really don't think GF will be changing their process just like that :/