My friends and I had something along those lines around the early 2000s built with Linux firewalls and freeswan IPSEC tunnels. I sure do miss the old vibe and chaos of the early internet.

Bit by bit the tunneled WAN thing sort of became irrelevant as we built more stuff as internet facing services, to the extent that the fun parts were more likely to be installed in a datacenter somewhere than sitting on the LAN at our houses.