Any time you make the existence of one relationship a condition for the existence of another -- any time you say "lf you want to be with one of us, you have to be with both of us", whether to a single person or to a couple, you set yourself up for 50 kinds of pain, imho. Some relationships succeed, others fail, that's just life. As such, predicating the existence of relationship X on the success of relationship Y just ends up being cruel for all involved. That's based on everything I've seen from years doing poly and reading here. I would strongly advise against it. There's nothing wrong with stumbling into a triad or quad, but trying to build them goes badly.
I encourage you to do a tag search for "unicorn hunters" for more perspectives. Also, a number of us theorized extensively on the topic here: http://www.polyamory.com/forum/showthread.php?t=23779
Best of luck in whatever you decide to pursue!
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.