Ultimately I think that labels live and die in the marketplace of ideas. My gut is telling me that since the Lifestyle is tiny and fragmented already, and that the number of those willing to define themselves via someone else's label is likely pretty small, the likelihood of progressive swinging/er joining the mainstream lexicon is slim. Regardless, I don't think as a term it is likely to dangerously confuse anyone, and at worst it would simply spawn a question: "You call yourself are a progressive swinger, what the heck does that mean?"
If the Swingset crew think it correctly encapsulates how they feel about their approach to ethical non-monogamy, and gain a sense of empowerment using it as a banner, I have no problem with that.