He didn't have one? Why isn't it coherent to you? I find it very coherent.

They seem to think Sephiroth wanted to destroy the world, considering this isn't the case might explain that instantly. Well technically.

Things that they need to keep. xD

He went insane, he wanted to become a god, and he wanted to exact revenge on humans. He wanted to exact revenge by destroying the world... and he was still in it by the time meteor was about to destroy it.

You could say he became a "god" or "semi-god" or whatever you want to call him and that would have given him the power to survive the destruction. But he was killed by a spiky haired guy and his overlimit. A little bit more explanation or clarification or a more coherent reason for him to go through all that trouble would be nice. 

Then again maybe I'm wrong, and I just didn't understand the overly complicated storyline.

All fantastic news. c:

Meteor as not summoned to destroy the world, just injure it. He wanted a wound like North Crater but bigger where the lifestream would gather to heal it. He would then absorb this energy and be like a god, killing everyone and carrying on where Jenova had left off. The world needs to remain for him to do that.

Sephiroth had a distant personality. He had Jenova's cells from birth. He read about who he was and who his mother was. He took Jenova's destructive way of life and decided to cause a huge damage to the Planet and be there in the center to absorb the Lifestream the Planet would use for healing itself after Meteor would hit the surface. The world wasn't meant to be destroyed, life on the planet was on peril and maybe the Planet would have been unable to heal itself after Sephiroth would channel all that energy, but that was more like a secondary effect of Sephiroth's plan. 

You are right about the lifestream part. I recall something like that but I'm not sure if the reason for him beoming a god was that. In fact I think they never explained that in the game.

I always saw Sephiroth as a talented guy in battle (for his genes) who never found a place for himself among people. Then he learned the story behind Jenova and found a fucked up purpose in his life. Remake does leave a chance for writers to add some meat to his story though, like a subtle calling from Jenova through her cells in Sephiroth's body for him to continue her life's work and of course set her free.

I hope they focus some of their attention on that, the story in the original was good but it wasn't very clear, that could be fixed entirely with the remake.