I was wondering a little bar next each enmity meter.
Red if you are first in mob enmity list green otherwise

Bar Full Red = you have 1000+ more enmity than the 2nd character on the mob enmity list.
Bar Full Green = you have 1000+ less enmity than the 1st character on the mob enmity list

so when bar depletes you know if you are losing aggro i you are a tank or if you will be in trouble for the others.

Something like that