From what you say, i assume you'd mean something like this?
http://img834.imageshack.us/img834/623/targetwindow.jpg
Forgive me if its a little messy. Basic structure is;
Coeurl A above list = Current target
Red = Engaged target
Blue = Moused over
Green = Targeting you
Although i feel like the tab targeting has to be sorted out properly, i do think that having something like this (as an optional toggle) would benefit some people. Its true that its a bit of a UI hog, although im sure SE can do a better job with the real thing than i can with photoshop lol, but for battles with lots of enemies i think it would save some frustration.