Speaking from personal experience, I think opening to poly from a monogamous relationship inherently carries couple privilege, no matter how hard they try to avoid it.
Well yeah, but I think it could be worked with instead of against. Like with the dedicated solo poly who is ok with a season or two of casual love with a married person or a married couple, or even a two-couple quad.
I thought one of the things that made my quad work pretty well was that at the time, no one really needed to move in with anybody, it was kind of understood that Fire and Hefe's marriage was a solid, primary thing, and while I expected that either of them would put the other first if need be, I didn't feel that it in any way marginalized or diminished my place in the relationship. I was solo poly and so I was ok with how it was.
Honestly my eventual feeling like a "tourist visiting their world" was as much a matter of geography and time, as it was any kind of existing couple privilege. It was a non-issue, in my mind.
I guess they had couple privilege but I didn't want it. It didn't matter.
Maybe it just depends on what people's expectations are.
But then I think of how easy it was to fall into poly with Analyst and Hefe and Fire, as a quad...and I consider the idea of trying to open the closed, mono relationship I have now with Zen and I just imagine such a minefield of hurt and frustration and difficulty and issues, that it's not worth it. And why would it be, if we're both satisfying each other very well? *shrug*