Restricted Cast, who would you pick?

Fair point.

I doubt I'd actually set up a hack like this. I'm using it more as research for what I want to do with an FF1 plot. I want Sara of Corneria to be important but not playable, so my thought was that she'd be the only one who could USE crystals (thus being the character displayed whenever a summon is activated in combat). The principle seems like it would work with Terra as well, supposing you didn't want the Espers to be able to manifest once they'd perished (it'd be Terra releasing the power in the magicite instead).

In some ways, that puts her in EVERY party, but in others it marginalizes her role in the actual gameplay. I'm not sure how I'd feel about that, I have to think about it more.