I had some fun with this as well a while ago. It's too bad that with IPv6 we'll only get one loopback address (i.e. ::1) and not again a whole loopback subnet.
IPv6 has a humongous private network range, though. fd00:/8 has 2^120 IP addresses. You could set up a Docker bridge with that range and run containers with random addresses. Correctly guessing one of 2^120 addresses would be nearly as difficult as cracking AES128.
