How about a backpack version of the shopbag? One that folds into itself.
This would be great for business or light travelers who find themselves with free time and want a daypack but don't necessarily want to travel with something like the Synapse. It wouldn't be meant for serious hiking but just for a day out in a city. Big enough to hold the basics and of course, the magical o-rings.
I got the idea seeing these two items:
They wouldn't have to pack down that small--I have a similar item and the material is very cheap--but pack down into a small pouch would be great.
I'd prefer a Tom Bihn version.