FFVI Worlds Collide

Request: Allow Banon and Leo to be recruitable and playable as long-term characters.  Let us change their gear and espers.  (For the sake of ease if it isn't already in-game, assume Leo can wear the same stuff as Celes and assume Banon can wear Strago's gear.)  Perhaps allow players to select a maximum of 14 playable characters when seeding a game, or use Banon/Leo instead of Umaro/Gogo.

This is a tall order, perhaps too tall.  The Guest slots that temporarily store Banon and Leo are not as usable as they seem; this community spent years trying to get the first of them to behave (do a search for Iris Havengard on the main page).  PowerPanda picked up the project and is currently the closest to sussing it, but it's not an easy road.
Setting up Banon and Leo in Gogo's and Umaro's actor slots is a more reasonable approach; there's already code available to give Umaro a command table and removing his tackle/blizzard/toss attacks is relatively easy.

GrayShadows also set up a RAM repointing to allow Gogo a learnable spellset, so the legwork is basically done in that regard.
There isn't enough contiguous ram to allow Actor $0D's slot to learn magic though, sorry.  MMMMMMagic can allow a shared learnset, but without that the best you can hope for is Gogo-esque magic (spell list comprised of all other actors' lists in the party).

Although... Leo refused magicite and magic injection, so it's reasonable that he wouldn't take an esper and that he'd only have 'party' magic.
If Atmatek expresses interest in the idea, I can list the addresses that need tweaking and the patches that would need to be applied.