Multi-Party mode

There are a few points in the game that you can place characters into up to 3 groups and use Y to switch between them. 

Is this a feature that could be added to the entire game / is this something that has already been explored?

I would love to be halfway through Doma castle and switch to my second party climbing the Tower of Fanatics 

I’m wondering if this has been done / is even possible / would be way too much work to implement