Agree with the OP that this would be a nice feature. After all we can switch out our party members, why not have spare PCs we can switch out? No need to change the story for them as we're ALWAYS the main character. What one experiences the others experience.
Currently having this issue. My wife wanted to try it out to see if she liked it. We did a multiplayer game, she didn't enjoy it so got a refund after only playing an hour. Now i am stuck with her character in that game.
At least BG3 has profiles.