Theories abound. The secret ending was pretty to look at but I doubt it means there will be a sequel. It's like fire, nice to look at but you wouldn't want to touch it.

As much as I would like to see a sequel, I believe it would be likely to become a huge flop, although there is a slim chance that it is actually an agreeable sequel. Square currently seems obsessed with Final Fantasy VII, I would not be surprised to see FFVII-2 with the reawakening of Genesis or some other character. If they do do this I find it unlikely that the main character will be Cloud or Vincent(they've been used, time to get in some fresh blood). In FFVII-2 the main character will be totally knew or at the least someone not within Cloud's group. I believe Square has expunged as much as they can out of that particular angle. If a sequel is made there will be new characters with small cameos of Cloud's gang here and there. Just an idea, I do not believe they are done with the world yet and will be doing more to it in the future.

I went totally off topic for a moment. The secret ending was probably just for Gackt fans and will not lead to anything...although the possibility of Genesis does remain strong. Genesis has reawakened whether he is the main villain or not is unknown he may merely be a pawn. If they use him at all. I do not think they're done using that specific world though, and if a revised version is done for PS3 it will surely bring more fans and thus enters forward to the inevitable sequel. Only time will tell.