What about adding an additional target window to the UI. Make this target window be the target of your selected target.
For example: I have targeted a Terrorweb Dryder and he's about to cast Meteor Shower. I don't have an interrupter to stop it and don't know who it's being cast on. If I had an additional window that can tell me who the Terrorweb has targeted I could warn them about the Metwor Shower so they could run away from the group so they all don't get squashed.
I dont think its needed either. The idea of an AoE skills is that you do some damage to more than one foe. Most players will notice when meteors are landing on them, taking damage and getting knocked down.