I would even go a step further and propose a unified mesh network, much like the wired internet. You could even be at a distance and as long as there's mesh hardware around (even if it's not part of your own coop), they could still route for the area. If you're a bit farther, you can use a directional antenna, much like wifi at longer distances these days. Heck, the coops would be just access services within the unified mesh network. Infrastructure cost would be minimal since the cost is really shared by every point in the mesh, and it's basically the current cost of a wifi router in almost every home these days.
There would be some routing overhead and obviously some heavy users, but on a mesh those are actually easier to identify and potentially isolate and route around. It's basically all the pluses of a open wifi hotspot, but without the security minuses. I can't wait until the 802.11s draft is completed and I really think that's the future of mass wifi access.