My home wifi barely stretches 50m down the road (yes I know they mention Bluetooth, but bluetooth is even worse in this respect). Meanwhile you can get outdoor wifi repeaters within the allowable output in the 5GHz channels in the UK with ranges in the 1km-2km range that are still cheap, and directional microwave equipment with theoretical ranges in the 100km range (major limit there is going to be height - beyond a few km, the curvature of the earth becomes a major hassle unless you can go higher gain).

Without that kind of distance, you need massive penetration to be able to connect users at all, even if you aim to pass data over the open net as soon as you get data to a node that is connected.

I live on a relatively high density London road, and I can typically see maybe 10 networks at any one time when travelling between home and my local train station for example. There'll be multiple devices on each, but with that kind of visibility it'll take a large proportion of users signing up to a service like this before you even start getting any big benefits from it.

I do believe peer-to-peer setups can make sense for this, but unless our smartphones gets massive upgrades in terms of antennas etc., I think building something around higher gain outdoor wifi will be more likely to be viable.