While the retaliation concept is nice (provides a way for higher level players to attack lower level ones), I fail to see how much benefit it is going to provide.
In the cases provided in this thread, if gorlin or Ahazz were to retaliate against me, chances are they would lose, as I have already demonstrated that I can beat them.
The only benefit would be for them to power up (ie legendary items) and then retaliate. Though another benefit would be for them to get gold from me as well.
I'll second (or third, forth, etc) the retaliation concept - I do not think a lot of games have so it would be something different.