> That is simply not true. We had one bit left (the reserved/"evil" bit) in IPv4 headers […]

Great, there's an extra bit in the IPv4 packet header.

I was talking about the data structures in operating systems: are there any extra bits in the sockaddr structure to signal things to applications? If not, an entirely new struct needs to be deployed.

And that doesn't even get into having to deploy new DNS code everywhere.