Something I didn't see mentioned in the piece that I see as THE major hurdle to that noble, if utopian, idea is that more and more ISPs in the US are capping bandwidth (Comcast, AT&T U-Verse to name the biggest ones). I guess you could have a setting at the router level that could be used to limit the amount of data going through the open part of the WiFi but I still don't think most people would agree to that kind of selfless generosity. In any case, no such idea can be implemented while the capping issue is left out of the equation.