I don't think I'd ever want that. I'm sure there's gonna be girls that might say they'd love to do it, but I just can't agree with it being something I'd try. Personally, I don't like multiple partners to begin with, and I just think sex is too personal to me to be doing it with someone I'm in a relationship with, and some other person at the same time (friend or stranger, it doesn't make it any different to me).
And I really don't think I'd want anal and regular sex at the same time. As aquamarine mentioned earlier, when you think about the realistic side of it, and the physical stretching that you'd go through, it's just something that guys involved would want way more than girls. I think that's something guys never really consider about a lot of these kinds of fetishes.
Even if the DP was vaginal and oral, I'd probably still have a problem with doing it, just from the two partners part of it (again,that's just a personal preference).