[jovial_cavalier]

Your full name is not the same as your local IP. Since your NAT subnet is almost always /24, there really are only 256 local IP addresses. Which one you happen to be using at the time is not really important. There are 10,000 other things about your browser that could be used to uniquely identify you. This is a feature of WebRTC that allows it to do what it does, not a bug. If you are worried about 3rd party web apps sniffing your local IP and somehow using that info against your interests, don't go on the internet.

[BeefWellington]

If it leaks local ipv6 there may not even be NAT involved. This would unmask the user on the other end of a VPN or Proxy, for example.

While this generation is done only for IPv4 space someone with sufficient time, resources, and inclination (say a large Ad conglomerate) could similarly start generating these for IPv6 address spaces.