I love this idea and have considered doing something similar with friends for years. It’s cool to see how far they’ve taken it — much bigger than I had envisioned.

My biggest/only concern - which they gloss over, mostly — is security. Combining networks puts added responsibility on every family that joins. What if friend-X’s kid downloads a virus-riddled torrent, which is capable of multiplying across hosts?

Your own hosts/perimeter can always be protected, but there’s a loss of control with this setup.