Some of the mainline games are MMOs, so cant really be covered. As such, important spin-offs and sequels, such as FFT, are considered as replacement.
Well, I, for one, would be there to see Omi devoting years of his life mastering solo play in a dead MMO.
As mentioned, both have excellent gameplay, but I find that FFV has more replayability, and additionally, the fact that FFV forces the individual members of the team to develop a personal identity through mechanics is something that I find better. As for story, while it's true that FFV is a much more simplicistic, cartoon-like narrative, my opinion is that it actually performs its own particular narrative goal nearly flawlessly, whereas FFVII has a lot more stumble on it's (admittetdly vastly more ambitious) story. So... I guess I think that, when judging a game's quality, while ambition and execution of those ambitions both matter, I value the execution a bit more highly. I also think that FFVII, while it does quite a lot with the tools at its disposal, is visibly harmstrung by its need to experiment with new things, whereas FFV makes a much better use of the (yes, inferior) tools at its disposal, which I also value highly.
I think FFV fails in the context of this thread specifically because there just isn't that much to talk about, narratively (aside from Inexplicably gender). It's a simple story executed well, and that's the long and short of it. Unlike early games, it's defined enough that it's hard to go on wild tangents about the role of monsters and the secret history of the world (though Omicron does try), and unlike later games, it doesn't try to talk about Big Important Themes, well or badly. It's fun. The end.
More fodder for the hypothetical FFVI Remake: What if you just don't fight Kefka at Narshe? Introduce one or two more Imperial minibosses, and have them take the fall in that particular battle, and earlier when you face Kefka at the siege of Doma, rather than him running, make it more explicit that he's misleading Sabin/Shadow with illusions, which will serve double-duty as foreshadowing the confrontation with Leo.
Eh, I think Kefka being full of hot air and crumbling instantly when met with any kind of resistance is pretty important to his image, and making him a legitimate powerhouse from the start would detract from it.
As was discussed back then, the solution is simple: add a scene where Kefka or Banana Mengele reads the data obtained from the party's infiltration of the esper lab, which allows the bad guys to make a breakthrough regarding magicide and devise a way to forcibly convert espers into powerups for Kefka. It honestly wouldn't take that much effort to plug in this plot hole, which is what makes it annoying to begin with.
Clearly, it was a missed oportunity that the few FF crosses only have Taylor get super op by giving her/become All The Summons/Primals (and then sum magik) instead of giving her All The Mastered Materia.
Ah, but you're forgetting the first rule of good Worm crossovers: Taylor's new powers should be creepy, as it's an essential part of her appeal.
Fortunately, FFVII has no lack of horrifying imagery to draw from, some of which is even directly connected to its protagonists.
Which is to say, Taylor should get the power to control chocobos.
See, canon Taylor is regarded as creepy because she's constantly surrounded by bugs, allowing them to crawl in her hair and clothes. She's also ruthless, going for the eyes or choking people with flies.
FFVII!Taylor would be creepy because she makes chocobos do incest.
I have absolutely no doubt in my mind that they'll nail Sephiroth, they've already done so in the first game and I can't imagine they won't continue to do so in the next.
But will they nail Shera (and Cid, I guess)? That's the real question.