OP wants a mesh network. But Wi-Fi is not a mesh network implementation. Also, Xfinity is a terrible example. As far as I know, the publically-open side is a s

OP wants a mesh network. But Wi-Fi is not a mesh network implementation. Also, Xfinity is a terrible example. As far as I know, the publically-open side is a separate signal with separate bandwidth allocation. It does not use or effect your paid connection at all. Hence why one can set up a wireless router to bridge the the public network into the private one for extra free bandwidth. This also alleviates all of OP's concerns. Bottom line is that people pay for internet access as a resource, and people are generally not in the habit of giving away paid resources for free. The only way this will happen, IMO, is a municipality or otherwise large funded entity taking it on to provide free access to a wide area.