Junon has a bit more going for it than you seem to remember. First you have to save the little girl to get the dolphin to be friends, then Cloud has to pretend to be a soldier and practice for the march, then you get to explore the town a bit which is probably the third largest city in the game only behind Midgard and Gold Saucer, Then you have to do the mini-game for Rufus and finally you get on the boat, which I would count as part of the chapter as I feel the Jenova battle is a good stopping point. My reasoning for Junon though is that as I pointed out, there is a lot of stuff that can be expanded on here. You're mostly stuck as Cloud for the whole thing in the original and if they wanted to make Junon its own chapter there is enough potential content to do so if they simply expanded the scenario to explain what everyone else was doing at the time.

There are a lot of locations like this throughout the game and depending on the story to game ratio of each episode, I don't feel its out of the realm of possibilities this series will be longer than people think it will be. I would say Four Chapters is a reasonable number but that's assuming the games drop certain locations, quests, and the world map to make up for all the expanded scenario stuff and minimize backtracking. Personally I feel six or seven episodes may be more likely for the project, not simply because of a cynical cash grab, but because there are a lot of lore rich parts of this game that seriously under-peformed in the original, and if they want to fix those in the remake, they have plenty of space to do so. If they can get the games released on a annual or semi-annual basis, then I don't feel it will be a problem for fans depending on the quality and price range of future installments. The real big x-factor in all this is whether they're going to be forced to retool the game engine due to feedback. Serial chapter installments work best if the core gameplay is good but if there is some major flaw or fan backlash to some element of it and they try to fix it down the road, it will likely cause delays.

I feel you're overestimating how long Midgard really was. I mean Reactor 1 attack, return to sector 7 to meet Tifa and get some backstory, next Reactor mission, meet Aerith and escape the Turks, cross-dressing event, Sector 7's destruction, break into Shin-Ra, get captured, break free and meet Rufus, big escape. Midgard is pretty dense in story, but its also incredibly linear and there isn't as many areas in the original since you do backtrack quite a bit but its never a big deal since you can get from Aerith's church to the back end of Wall Market in under ten minutes. The longest section itself is actually the cross-dressing mini-game and the Shin-Ra tower, but even with a little level grinding, it really should take you less than ten hours to complete Midgard in normal play for the original game. It's one of the few decently paced parts of the game.

I'm honestly more interested to see how they'll approach the back half of Disc 1 and all of Disc 2 since I feel like the locations get less and less time spent there once you leave Cosmo Canyon. As I mentioned before, not a whole lot actually happens in Nibelheim outside of the optional Vincent recruitment quest, but I really feel like that's going to be a place where we're going to see some more heavy handed changes. Rocket Town is short, Wutai is optional and then we're just wandering around looking for the Temple of Ancients which is basically the last traditional dungeon on the disc before we get to the big boo-hoo scene. I still feel like we may see them skip over places. I feel Kalm will likely get dropped as well as the Mythril Cave. I can also see them skipping over Fort Condor and just introducing it when they do the Big Materia quest because that place is basically just a mini-game hell hole to begin with. I also feel like Mideel will be a place you see in cutscenes, but never actually explore. I still imagine Yuffie will be recruited before Junon. I also don't see the whole Big Materia quest will be a one disc deal since Cloud's true backstory is a giant momentum killer in the middle of the quest and will likely be stretched out a bit longer as well. Oddly, I feel the one really major change from the original I can see happening is dropping the Northern Crater as the final dungeon and simply have Sephiroth either manifest in Midgard to face the party and get a front row seat for Meteor or simply have the party use Midgard as the entrance way to face him. Midgard is so iconic to the game, I could see them making it the sight of the last battle and it gets around one of many minor plot holes about his plan.