Changed my vote to the Northern Crater and am about to throw down some major speculation.
Like Remake before it, I think Rebirth's plot will generally follow the original game's, though it'll build up its own mysteries. Instead of the Whispers we'll have Zack. Also like Remake, the biggest deviations will occur late in the story, starting with Aerith's survival at the Forgotten City (don't @ me!) and ending with Sephiroth's new "endgame" being revealed at the Northern Crater. I'm betting this endgame will involve something a whole lot bigger than just Meteor.
On Aerith living: in Remake, Aerith has the ability to pass memories/feelings to another, as seen with Marlene in 7th Heaven. To me this is like chekhov's gun. I doubt its only purpose is to calm down children, especially since Marlene was just about to say something revealing before Aerith shushes her. I imagine at some point this new ability will be used on Cloud, whether intentionally or by accident. He'll fight to save her and succeed. However, the story isn't over yet.
On Sephiroth's endgame: I'm a multiverse guy, so buckle up non-believers. To be more specific, I think the universes experience time differently, as in December in the Beagle universe (Remake) is occurring simultaneously with September in the Terrier universe (Zack's last stand). As we know, the goal of the Whispers was to maintain the events of the original game. To ensure the planet is saved from Meteor (presumably). However, now that the Whispers are defeated, things may become unstable. I imagine Meteor is starting to destroy the planet in other universes. Remember, I think the universes are at different points in time, so some may be as far as January when Meteofall occurs. With each planet that is destroyed, Septhiroth absorbs it and grows stronger. Sort of like an inter-dimensional Jenova. However, unlike Jenova, he's not doing this without reason. As alluded to in the Edge of Creation scene, there's something out there that Sephiroth is fighting against. I think his endgame is to grow strong enough to resist "joining" whatever that is, as he put it.
Though the party saves Aerith at the Forgotten City, their victory begins to feel hollow as they imagine the countless planets that have been lost to Sephiroth already. Ultimately, saving just one Aerith is futile.
We lose Cloud, Meteor is summoned, the Weapons awake, Zack is involved, cue Part 3.
