I've suggested this in discord and a lot of people seemed to like it. Many missions have very dynamic maps. The same antagonist that might be good at the first section of Enemy Within/Beast Lair, which are huge open spaces, are likely not to be so good on the second part, which are small maps that allow raiders to dogpile you.
There is an old trailer when Konstantin confronts an Uras acolyte and it is pulsating and shapeshifting between forms. Being able to switch between characters either between respawns, or between scene transitions, would not only be lore-friendly, but also help those who might be bad at initially picking, or to adapt to the Raider's play style.