I'm almost certain nobody has done this.
I think for this to work better you'll probably want more common, but weaker damage instead of egregiously powerful and egregiously rare effects. Right now the desperation attacks are so rare that new players probably don't even know they exist, while veterans who do know they exist can dole out over half a boss' HP in the WoB. That's fine for the JRPG style where Rule of Cool generally trumps game balance (which is okay in itself), but since you're trying to make it a usable game mechanic that's probably not what you want. Of course, you probably won't be deciding the power entirely anyways because the hacker using the patch could probably adjust the power to adjust for their game's sense of scale.
While FF8's Limit system is closer to FF6's than FF7's, FF8's Limit system was extremely abusable, and I'm not really a fan of it. FF7's is definitely a lot better if it's manageable, at least if I'm going to be lazy and just say "Do what that game did in this game". I can't think of a fully functional unique system off the top of my head, I'll probably do some more thinking about it later. Preferably it would have some way of scaling in the endgame, but that might be really hard if you're not using extra space...
I think for this to work better you'll probably want more common, but weaker damage instead of egregiously powerful and egregiously rare effects. Right now the desperation attacks are so rare that new players probably don't even know they exist, while veterans who do know they exist can dole out over half a boss' HP in the WoB. That's fine for the JRPG style where Rule of Cool generally trumps game balance (which is okay in itself), but since you're trying to make it a usable game mechanic that's probably not what you want. Of course, you probably won't be deciding the power entirely anyways because the hacker using the patch could probably adjust the power to adjust for their game's sense of scale.
While FF8's Limit system is closer to FF6's than FF7's, FF8's Limit system was extremely abusable, and I'm not really a fan of it. FF7's is definitely a lot better if it's manageable, at least if I'm going to be lazy and just say "Do what that game did in this game". I can't think of a fully functional unique system off the top of my head, I'll probably do some more thinking about it later. Preferably it would have some way of scaling in the endgame, but that might be really hard if you're not using extra space...
Moogles FTW