If it ever happens to us, chances are it will happen by accident. Milady very likely does not like the butt play too.
I don't think it will ever be 'clean' enough of an endeavor to pursue- it just sounds kinda nasty to deal with the brown stuff and the smell. And I'm pretty certain we'll never be doing enemas, so that pretty much isn't something I can see us going for.
Best of luck for those who try it and like it though, I guess
Shouldn't there be an 'Anal Sex' sticky by now?