The scene described in the first post is an intense turn on for me, but I never required this of my sub because of health reasons. I don't have any strong views on whether it makes for the perfect sub in some general sense. But certainly the willingness to go there is something I highly prize in a sub, although not something I would take advantage of without some health precautions. It's all about the mindset...

Re ass play and health issues more generally: my (now, sadly, ex-) sub was an anal slut. We didn't do ATM (because of health reasons), but we did both do a lot of rimming (or more accurately, anal tongue fucking - she delighted in getting her tongue very deep in my ass), without preliminary enemas or anything, and there were never any health complications.

That being said, maybe we were just foolish and lucky...