@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.
@DragonCamo -
I don't think that they are mega evolutions, but I do believe that they are new forms due to the terminology used to refer to them by the Japanese arm of The Pokémon Company.
(they refer to them as "never before seen Pokémon", which, as I pointed out in the first post, is the same terminology used to refer to Black Kyurem, White Kyurem, and Mega Mewtwo Y)
Also, they do have a few other differences aside from their markings.
(i.e Groudon has the symbol for Omega on his arm, and Kyogre having a symbol on his head and those big white dots (I don't know the correct term) having a "tail")
Also, Groudon is the only one that had black markings, as Kyogre's were red.
(sorry for using "also" a lot

)