The mesh organization will be a 501(c)3 but will not own the mesh routers. The mesh hardware will be owned by the community that makes up the mesh.
The exit nodes will be owned by the 501(c)3.
With regards to running exit nodes, Noisebridge, another 501(c)3, already runs a Tor exit node which should be legally similar to a mesh exit node.
Some links of interest:
- NoiseTor wiki page
- NoiseTor website
- NoiseTor FAQ
- Tor Project's Legal FAQ
- Tor Project's Abuse FAQ
- Tor Project's DMCA Response Template
- NoiseTor how to deal with the FBI
- EFF's Tor legal FAQ
- EFF's list of Good ISPs
If nodes are not owned by an organization, then some other way of agreement of how nodes should be operated should be made. One approach is to see each node as being peered with others and create agreements about how the rules the traffic should go over those links. Another is to extend such agreement into a license and also add rules about how the nodes themselves should behave.