I would argue the major issue with this is that it might not actually be mechanically feasible within the game engine and even if it was it would be an epic amount of work to make the change with a questionable amount of benefit. That's not even really taking into account party balance. Healing in particular would probably need some tweaking because the increased difficulty for healers would be directly balanced off player performance so one extra good player would make little difference while one extra bad player would add plenty of additional work.

In the end I doubt we will see this happen.