Yeah, this is the strongest suggestion so far.
Nibelheim is tutorial. Northern cave is the final dungeon, just how it was like in the original. Have some sort of Jenova or Sephiroth final boss.
Then part 3 is a Tifa game. Opens with Weapon attacking. The Weapons are the main plot point, with Meteor. You learn more about Holy and what could happen when it meets Meteor.
I've said for a long time that a good way to think about the split - and how hopefully they have - is what your three-act structure is within each game. This is where FF7 is in danger, because it's the Hobbit movie problem - how do you split
one three act structure into nine? You need three stories, each with their own three-act structure that stands alone.
Obviously not all stories have to follow the standard sort of three act up-and-down, but the FF games typically do as they're not really all that sophisticated from a storytelling perspective (which isn't a dig - the stories are still great regardless. Complexity or sophistication does not equal quality, after all).
The structure I've been a fan of for a while does give a good three-act outline to the existing story with room for expansion and stuff. The second game in paritcular - rather than the end of the game, you shunt
that major scene to the middle of the game, where it becomes the end of the second act. Think of this as the moment where Luke realizes his friends are in danger in Empire Strikes Back and abandons his training with Yoda. Then you have the moment where Cloud goes missing, which sort of forms that ending moment.
That structure also has tutorials offered in quite a natural-feeling way, cos you've got young Cloud in the flashback at the opening of game 2, learning from Sephiroth, and Tifa as a leader for the first time and getting to grips with that at the start of game 3. But, as pointed out by another...
I like this split the best for 3 parts, but I've been thinking how could they possibly fit all of that into the second part in a single game. Maybe if they don't expand other parts of the game as much as Midgar.
But part of me WANTS them to expand every city, so I wouldn't be surprised if it takes more than 3 parts. So now I'm thinking what are the best splits for more than 3 parts, assuming every part of the game is expanded top to bottom.
The only issue, I think, is the size of game 2. That's a lot of ground to cover, a lot of assets to build... but the advantage of that is then that game 3 would be mostly asset reuse. Game 3 would be lighter on content, but you'd probably save stuff like a visit to Wutai, the final optional showdown with the Turks in the underwater base, and learning about Vincent's past for the third game to help pad it out.
I think as far as Game 2 goes, it depends. Junon will obviously be sizable, as will the Gold Saucer. But Corel and Costa Del Sol can probably stay small... and Nibelheim
should be small, as the whole point is that Cloud and Tifa are small-town kids. But yeah. It all depends on how they do it.