As most of us know, Double Tap was taken out of the game and replaced with Double Kill because the implementation didn't match what the term double tap is generally understood to mean. There is a situation currently existing in the game that I feel could justify the re-addition of the Double Tap announcement: when a player carrying Aegis (the item dropped by Kongor, I apologize for not knowing it's HoN name) dies twice in quick succession (i.e. is resurrected by Aegis and then re-killed). Double Tap could be implemented either when one player gets both killing blows or just for whoever gets the second, final kill.
N.B. I do know that Double Tap has been discussed to death, but I haven't seen this idea suggested before and I did use the search function before posting this thread.