ora2 does something similar but not to the detail you want
Set up MT windows for everyone "Tanking/Banishing" and you can keep on top of the health of all the adds in % form.
Mine usually look like this on High King Maulgar kill
MT1 - Steakums - HKM (100%)
MT2 - Thathius - Priest (100%)
MT3 - Nammon - Warlock (100%)
MT4 - Gaucamole - Mage (100%)
MT5 - Momokee - Shaman (100%)
then i have the MA at the bottom
MT6 - Lastexit - (Whatever he is targetting)
Now in the spot that shows MT1-6 you get the raid symbol of the targetted mob and as the health goes down the MT windows show % health left. I know it's not exactly what your looking for but it's really as close as you can get.
Other mod, that is similar again is PerfectTarget but it doesn't show % of health just who's targetting what
Prolly doesn't help but its a option.