An open source network, either regional or wide area, would be a very big deal for many areas. Being 4G compatible is nice, but even if it uses a different band (e.g., less stringently controlled WiFi bands) a mesh network would enable a lot of projects.

On the technical side, current SDRs are cheap and very capable. Unfortunately, for this to take off one needs a large network effect and should the technology take off it is easy for various three letter agencies to compromise, for example by inserting their own nodes. And as some uses are likely to be sketchy "because terrorism/pornography" is all the justification they will need.