We have had this talk. My husband doesn't specifically have a kink for it, but he was curious as well. In our case it was right off the table because neither my boyfriend nor I would have liked that. It depends on the persons involved. If all of you are ok with this, have fun. But if even one isn't comfortable with it, don't step all over him/her. This is about the comfort of all, not that of one. As far as I am concerned, there are some things that one has the right to protect. And privacy is definitely one of it.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.