tor test networks should allow IPv6 private addresses
net/nodes/003br/notice.log:Sep 25 09:42:34.000 [warn] Unable to use configured IPv6 address "[::1]" in a descriptor. Skipping it. Try specifying a globally reachable address explicitly.
I'm sure there's a tor option that allows private addresses in descriptors for IPv4. It should do that for IPv6 as well.