I've just fought of another possibility.
Like I posted on third game speculation thread new form of Kyurem most probably will be combined with Reshiram and Zekrom. So that means both of them would must appear in movie 15 if they want to show new form of Kyurem in this movie. But they just appeared in movie 14!
We know that movie 15 will feature old Kyurem, Musketer trio and probably Keldeo. I think it would be too much to put along with them Reshiram, Zekrom and new Kyurem in one movie.
What I think now is that in movie 15 they will just show old Kyurem and Musketers. They all are available in B/W. Keldeo in not available but it's hidden in B/W scripts so they could just make Keldeo event without releasing Grey.
I think now that it's possible they will release R/S remakes on their 10th anniversary in autumn 2012 and later in July 2013 they will release movie 16 with new form of Kyurem, Reshiram, Zekrom and maybe Meloetta and Genesect. And finally in september 2013 they will release Grey. I don't think that Hoenn Pokemon will appear in any new movie or anime episodes because it would ruin Unova's separation from other regions. Do you think it's all possible?