I'd like the ability to cast a spell on a unit I don't have targeted by means of a "targeting cursor" if my current target is illegal. This way, I can keep a mob targeted (for ease of interrupting and that) but still heal the group.
Also, it would be great if companions in a group setting had their own unit frames instead of the tiny frame underneath party members. They'd be much easier to monitor and heal that way, especially in debuff-intensive fights.