Expanding the game in this way isn't difficult, as Midgar (and FF7's world in general) is a rich place with lots of empty space in terms of both lore and geography that can be filled in. It's relatively easy to create content to pad it out, it just requires the resources and effort.
Doing this without obliterating the
nearly perfect pacing of FF7 is, however, the question and problem. FF12, 13 and 15 all suffer from pacing problems too, imo, as I think they've never really managed to get the pacing nailed as these games have changed as we've had more realistic visuals etc.
But I do think part 1 will be Midgar. My prediction would be three games, a trilogy - they name-checked FF13, 13-2 and LR when they were explaining how the split would work, after all - and if I was splitting it three ways, here's what I'd do:
- Part One: Midgar, with expanded elements of Midgar as a semi-open world. Explore the sectors in more detail, undertake side quests. And a major area for expansion - actually explore city life above the plate, as you never do in the original FF7 (and we saw a shot of Cloud walking around above-the-plate city in the 2015 trailer, so presumably this is a thing). Above the plate was expanded more in the compilation, especially CC, to the groundwork is laid. End with the crew looking out over the world before them after leaving Midgar, a new mission in mind.
- Part Two: Cold open into the Nibelheim Flashback. The Nibelheim Flashback can serve a similar sort of purpose to those training wheels first missions in Mass Effect 2/3 - to remind returning players and teach new players the basics. Except this time, your experienced tutorial character who explains stuff to you isn't Barret... it's Sephiroth. It's also perfect for getting people up to speed - after the flashback, the party sit in the Kalm Inn and formulate a forward plan and recap what happened in Midgar. From there, continue on as in FF7, expanding a little here and there and folding Yuffie's recruitment (and maybe Vincent's, though he could slot in just as well later) into the critical path. End when Cloud hands Sephiroth the Black Materia in the crater and disappears, leaving the party in disarrary (thus you have your dark middle chapter and Empire Strikes Back ending - Aerith is dead, Cloud is missing, Sephiroth/Jenova has the maguffin to destroy the world).
- Part Three: Everything else through to the end, which includes a victory lap return to Midgar and open access to any area of the world from the previous game for new sidequests and distractions. Drop the optional stuff like Wutai into this part, too. Obviously the game opens with Cloud missing and Tifa as the protagonist, which imo is an interesting marketing hook - and it also again gives you a sort of 'in universe' tutorial excuse in Tifa learning the ropes of leading the group. It also means you save the money shot of the 'truth' of Nibelheim (and presumably bringing in some expanded elements from CC) for the final game.
