Good suggestions, all:
The poles aren't an end-all, I can definitely strap them to the frame. It's just slightly less convenient than the bivy. I have found that the less straps I have, the better, because I break camp in the morning without the ritual of tightening/checking/stowing loose ends.
It sounds like a non-issue, but I love the zen of simple bike touring. Having everything in bags definitely accomplishes this end. In a way, so does the bivy. No poles, stakes, rain fly, etc to deal with. Stop riding, sleep, wake up, ride.
As for the Revelate Harness, I would go for it, but my drop bars and cables are in the way on my adventure bike. Perhaps if I pick up a true mountain bike before the summer, I'll go for it. All my other bags are Revelate and I love them.
Oh, and as for the polycro, I am a paranoid guy with a deep love for keeping things looking new, so I'm going with a 9 x 4 foot piece of kitemaking tyvek instead of polycro. Adds a couple ounces, but it's bulletproof to protect the bivy or tent from puncture. I have relied on it in the past and love tyvek for this purpose.