There's some really good work gone into mesh networks with radios over Wi-Fi. CJDNS comes to mind and there was a post a while back on here.
Either piggy backing off of that or having some sort of a fork might work. Bandwidth and legal issues around encryption become a problem, though.
Thinking about it, encryption is only an issue on the ham side, though. So you'd use packet radio to get into the BBS/remote system, all transactions within that network go through the encrypted layer, but when it comes back out to the packet connection, everything is in clear text. The mesh network would be the system used for syncing up all of the BBS'. CJDNS works access point to access point and also over the web as well, bridging areas where it just isn't possible to get a long range connection going, where the world wide syncing up of services would work.
Problem is that this requires another technology to rely upon and it seems hard enough to get someone into packet radio, never mind a mesh network. A person can but dream, haha.
Definitely an area of interest. I only know little bits I've read, not technically proficient enough to actually get something like that up and running!