Mr. Scott, you are probably done with your project, so this is for discussion purposes, but I have always loved the idea of dual purpose equipment. Down jackets can be the top half of a shrunken sleeping bag...a poncho can be a sturdy shelter in camp, and an empty rucksack can be a sleeping pad for you legs. It's even been done for ages with capotes. Despite this, initially I baulked at the combination of those two categories of equipment. The disapparat needs they fill almost places them at odds, the exposure to the elements between pack disassembly and shelter construction among other problems seemed to advise against it.
Then I remembered a Discovery Channel show about survival in alaska only with the basics. I remembered them using a plain blue tarp as a wrap for their ruck sacks and fixing shoulder straps somehow. It struck me as painful, but they were packing easily 40 lbs +. It did seem very rudimentary, but also very organic in design. Tweaking the idea, a person could start with silnylon or even cuben if experienced in taping and reinforce it with strap attach points. You could shape it like a six moons, etc, and wrap all of the gear up in it and affix the straps for backpack use. You could use light weight silnylon bags or a bag for keeping the gear water proofed once out of the pack. I think if you started with the shelter that you wanted and then worked back toward the needs of a pack, you could end up with the object of your desire.
I am actually intrigued by this idea now. It could be reduced even further by taking a silnylon dry bag and making a set of nylon straps to make it a rucksack. This might defeat your purpose though.