Said UI could likely create a macro that would perform TargetNearestEnemy() as you press a movement key. There was a Priest UI mod that did this with Inner Fire, so it can be done.

!K_A!, it would have to work a lot like CT_RaidAssist in the manner of a private channel, sending broadcasts/etc over that. While possible, I don't feel that a mod of this type would have too much popularity.