I think what would almost certainly save and develop the fandom into new generations of any Final Fantasy world are new games that build upon their respective world's lore. For example, which FF world do I personally want to know more about? Ivalice. Why's that? Because a bunch of games are set on it, and there's a lot of mystery and wonder to it. Granted, I think the same of FFVIII's world, even though it is one game. Insert your favourite world here. New games don't have to solve those aforementioned mysteries and wonders, but add to them. Hell, create new regions that include old regions in an "inaccurate" way, leaving you to wonder what is true or not, and whether it even matters, as long as the current story being told is good. It is not like there isn't already fan theories about connections between FF worlds, given some similar characteristics in their maps. That doesn't ruin anything about the stories in the respective FF games.
With FFVII, make a subtitled FFVII with a new bunch of characters. Building lore and character classes (expanding on traditional FF jobs, using them as a guide, etc), and new areas, etc. Not over-explaining remotely anything like "And this is how Sephiroth got his sword!" or "and this is how Han Solo did the Kessel Run and met Chewbacca", etc, which tends to happen in media a lot these days. I'm talking about completely new eeeverything. Leave the old stuff as it is, referencing it only if necessary to the story, and make the new stuff equally as interesting.
Okay, so Jenova did X in ancient history (pun initially unintentional), but what about Y incident caused by Z entity that hasn't been mentioned in the franchise yet, featuring locations A through Z, also not yet mentioned, etc. Sure they didn't appear in the OG FFVII map, but neither did Healen Lodge until Advent Children, or whatever. Maybe find an explanation for why that is. Maybe Midgar is doing to The Planet what Esthar did to itself to keep these areas a secret. Maybe Wutai is behind it. Maybe it is another known or unknown state (or as said in first paragraph, maybe it doesn't matter). Fill out the world, make it alive. The additions to the lore in DoC were interesting, like Deepground and Omega. So was AC's Geostigma, and Rebirth's additions to the Gi Tribe lore. You name it.
Anyway, if Square were listening, that'd be my suggestion. They got all this IP that I feel they could be doing a lot more interesting things with.