...Some kind of control-related utility were added as a bonus to using each one. Not just simple "resist fire" for the fire control, but maybe something like increased regen, crazy fireballs, or even better bloodlust. The controls that see the least use could get the more desirable side-effects.

Also, it would be nice to see some synergy with currently-existing edges. For instance, if Hellfire could help out fire controlled unholies, it would really go a long way. As you know, once you hit 43 you are dealing with a whole new tier of enemies which can handle your damage output better, and some (like Maran, and invokers) can just negate it entirely. Since most AP's don't ever get beyond fire and/or ice controls, this would be a welcome change.