Do you think they will still do CG trailers? I kind of hope they do what The Last of Us did on PS3 and just use the PS3 assets at higher quality for the cutscenes. I'd rather maintain consistency than have a strange moment where Cloud and co look 10x better for a brief moment. Dunno if they will be able to have fire tech to do the Sephiroth scene justice though.
SE can create more fancy fire effect and record in-engine FMV that can be reendered at 1fps if needed. When all is stitched together, end result will be nice 30fps FMV animation.