Reading user329's question about running a secure email network using SMTP over Tor, I was wondering how standard email transport could be implemented among hidden services.
And then I remembered anoNet. Wikipedia says: "anoNet is a decentralized friend-to-friend network built using VPNs and software BGP routers. anoNet works by making it difficult to learn the identities of others on the network allowing them to anonymously host IPv4 and IPv6 services." However, if the underlying VPNs are routed through the Internet, there's little or no anonymity involved.
It would arguably be possible to create anoNet-style darknets based on Tor, comprising networks of Tor hidden services, linked by TCP-based VPN or OnionCat tunnels. Given such networks, implementing any Internet service would be trivial.
If such systems were implemented, would the networking overhead be unworkably large?
Such systems would facilitate high-throughput abuse of Tor. How could that threat be mitigated?