Seems to be semi-doable, if you have enough people running enought routers with the right software and the distances aren't too great. That's what is going to kill this concept, distance.
I have a hardwired network in my house. Installing a wifi router, given the depth of my house, distance to neighbors, will link me in to - two other people. Unless I get some big high speed low drag wireless modem, then maybe - three. Woo hoo.
Then there is security. Google potato chip can wireless antenna.
Good idea, would work in a densely populated area maybe. Not in the burbs where I live.