> You've perfectly described how registration numbers of cars were handled in USSR, for example.
Three points here:
1. USSR does not exist any more. This could be one of the reasons. ;-)
2. Cars with all types of regos could drive just fine. I cannot drive at all on this new IPv6 highway with my IPv4 address.
3. You are required to register you car every year. You are not required to register you net address every year. If fact, many people/orgs/companies had them for many, many years.
You see, where I live, people still have old rego plates. Like "4" or "6". And they still work just fine. We found a way to interoperate with new ones like "XYZ123". It was _very_ difficult, but it eventually worked :-)