There may be ways to overcome the limitations of mesh networking, as outlined by many people here, but you will need to think outside the mesh, so to speak. It is probably best to think of the mesh as the "last mile" component rather than the backbone.

One idea: a $5 laser pointer can be modulated at well over 100 Mbit/s. Everyone in an urban area who can see one side of a building can bounce laser beams off of it. (Data recovery and collision resolution are left as exercises...)