been just watching and now I am starting to think that remake is a sequel yet it is not a sequel in the traditional sense, if remake is anything it is more or less following xiii-2's time travel thing.
Let me say why, in ending in edge of creation sephiroth says seven seconds till the end enough time for you perhaps and tells cloud what he will do with it is up to cloud basically this indicates either this timeline sephiroth knows his fate or he is indeed original timeline sephiroth and came back in time to change his fate.
The other clue he is original sephiroth is chapter 2 when he tells cloud he can't save anyone cause he is too weak not even himself, another clue is how did aerith know Marlene's name? And Aerith puts a finger to her lips to tell Marlene to be quiet, also cloud's vision of aerith dying and crying is maybe not a vision but a memory.
Also aerith dream tells cloud not to fall in love with her even if he thinks it's real meaning yes cloud and tifa are romantically together in Advent children and yes cloud did love aerith even after her death of course that is my belief another hint is sephiroth when cloud says he killed sephiroth the sephiroth says." Oh need not remind me of our time together" or something like that then says that was then this is now.
Of course I am going on what I saw and read from various sources like whatculture.com and such but like whatculture said the ending is genius cause now it opens up various possibilities like preventing aerith's death and sephiroth being stopped early and so much more now that they have the knowledge of their original selves and such now they know what will happen and can possibly stop it before it even happens course his is all speculation on my part