I totally agree that the idea is extremely hot. It's fueled my fantasies over the years and it has obviously done the same for many others.
My wife is quite jealous and I'm convinced she would fight any woman she thought was fucking me (or trying to) but then she would come after me for allowing or encouraging it! I love the idea of her fighting a rival and wouldn't care if she won or lost but in the real world that can mean injury, police and other not so pleasant results. Still makes for great "pillow talk" though!