There is a noticeable tendency towards poly folk also identifying with some sort of additional type of "alternative lifestyle". One of the more commonly seen ones is kink/bdsm. It's been something that I've gradually delved into myself over the past several years, and find to be an element of my relationships that enhances the overall structures.
There can be a point of concern when the egalitarian poly outlook bumps up against the Dominance/submission element within a relationship that is both poly and kinky. S and I are both pretty switchy, so we just sort of pass the baton around on a physical level, and keep the relationship dynamics piece pretty neutral. D and I, on the other hand, have a pretty strong element of D/s in addition to sadomasochism, and poly.
This has all been going rather swimmingly, with only a few minor twitches where shifting from a role of Dominance/submission into being a self-advocating partner seemed a bit clunky for either D or I. In fact, the smoothness of those transitions led me to a place of feeling quite comfortable deepening that dynamic, so I recently "collared" D as my submissive. That wasn't something lightly undertaken by either of us, and one of the key conversations surrounding that choice was how/what differences might be seen within our poly framework by me stepping more fully into a role of Dominance, and he into one of submission to me.
What it boiled down to for us was that D/s doesn't replace agency and self-determination. I can be in charge, and still require D to participate fully in the relationship dynamic as a responsible partner. Part of his submission to me involves looking towards the well-being of the relationship as a whole. Submission isn't a license to put all the responsibility for making things go on my shoulders. For me, being at the wheel doesn't mean that a navigator isn't useful in getting to mutually agreed-upon destinations, or that I get to ignore it when my navigator lets me know that the road ahead is likely to be bumpy, it just means I get to pick the route that seems best, and if I flub things up, it's incumbent on me to get things back onto a useful track.
Poly and kink can coexist quite comfortably, as long as no one is abdicating responsibility towards themselves, or to the relationship as a whole. If something were to come up that was a significant sticking point, D and I agreed to have the poly model as the fallback position for conflict resolution. In the meantime, I'll just enjoy the reality of an eager, responsive sub that is choosing to be at my disposal as required, and all the responsibilities and satisfactions that go along with that, as well as valuing a loved poly partner!