ahh yes your right kishi i forgot about that. but i think there wouldnt be enough of it to be used by many people, so that could be another excuse not to see materia in the movie. well, ff7 left a lot of open questions, so you could probably come up with many many many hypothesies (plural?) and find at least one piece of evidence for it :D
well in the latest trailer he showed up, jumping in front of a building, then that building comes crashing down and you get a good shot at him. but its still unclear whether that was a dream (definitely wasnt a flashback), and if it wasnt, i dont think it would be the old sephiroth we know, since vincent said "they could easily make another sephiroth if they wanted to" (refering to the 3 bad guys)