They could put the icon next to the player portraits in the party member area. If you are the party leader then everyone could have an icon that you could see, if you are not, you can only see your own icon. Just a small little icon next to and attached to your portrait.
This way, it's not "dumbing down" the game as much (for those people who are saying it is), since it would only show that you had a certain level of aggro, not from what mob (assuming you are fighting multiple mobs). May or may not be a good idea, just thought i'd throw it out there.
It would help with "icon clutter" on enemy health bars though. Maybe.