It would be great. Suppose you could go in to an EX or savage with 7 phantoms, the boss HP fell at a set rate so no one had to dps, you could auto heal, and you'd just be there to dodge and survive. It would certainly make higher end duties more accessible so you could learn at your own pace without having to spend hours waiting around in PF, and when you did join a PF you'd have a better chance to progress and less time would be wasted.

It's never going to happen though.