There are situation where it would be fun to make a move together with another PC. This might be coop action, dialogue, combining cards. Right now the mechanics mean either taking action for another player (of course you can't play their cards) and possibly misplaying another PC/offending someone, or working outside Storium to draft up the play together. Multiple short plays don't get the same effect.

I think it would benefit the group's sense of shared purpose, and open up richer plays and PC interactions.

My rough thought would be a cooperative workspace where you could invite a subset of the group to develop a play. Each invited player could edit & play cards into it, and sign-off when ready--when all sign-off, it enters the game as a coop play.

I expect the rest of the group would see that a coop play is in development, though not the content.