While that would be insanely awesome, no, there is absolutely no way that will happen. Gray will be a third sister game like all the others, with aspects of both Black and White in it, although seemingly missing something, as always. But it will involve Kyurem more, just as the third sister game (minus Yellow Version) always does with the third, lesser-known about being of the trio. So no, not a sequel, just another remake, more than likely one that will be on the original DS platform and not specifically for 3DS (even Nintendo and Gamefreak know not to advance like that all of the sudden).