Hey Lazy, this is a bit late, but welcome to qhimm.
I am a big fan of your work with GSHI (if it is even still called that) and before entering the world of FFVII modification, I was using gameshark hacks from your site and anti-gsc.
If you are still interested in input for prequel ideas, I've always envisioned a Sephiroth's Story prequel based only on the information found in the original VII. This would primarily include:
-Sephiroth's role in the Wutai War
-Sephiroth's conception (Lucrecia/Vincent/Hojo's story)
-Ilfalna/Gast's story
Of course, these ideas combined with bits involving the Ancient Temple, Ancient City, Jenova's "calamity from the sky", the introduction of WEAPONs, some in-depth exploration of the lifestream (possibly from various perspectives), and even the beginning of ShinRa could make for a game that could rival the original VII. Zack's story need not be a major component of a prequel given the fact that the vast majority of the events that led to VII's story took place before Zack was involved, but some cameo appearances couldn't hurt.
I don't have much to offer in terms of scripting/coding, but if you needed someone to work on the kernel and scene for a potential project(s), I have a decent amount of experience (perhaps you've seen LostWing or Revisited?). Anyway, glad to see you here and good luck with any future projects - plz don't let them go to the qhimm graveyard.