Primary, Secondary, etc...
In my situation, should it ever go in the poly direction again, there'd definitely be a distinction between my foundational relationship and others. I do not think I could possibly compare an 11 year relationship built on trust, communication and commitment, to a new relationship.
I think, particularly given most upbringing and socialization in this country, it is easier for some to accept the idea of a primary relationship as it retains some of the perceived stability of a mono structure.
As far a secondaries, some have mentioned to me that being secondary might be some sort of slight, or raw deal. To me, it's just a choice. It also does not preclude finding someone else to enter into a possible primary relationship with (without sacrificing the secondary relationship)