IPv4 also hasn't been built with NAT in mind. And given the disaster it has been ... no, obviously, noone in their right mind would build a new protocol with NA

IPv4 also hasn't been built with NAT in mind. And given the disaster it has been ... no, obviously, noone in their right mind would build a new protocol with NAT in mind. For one, you don't need NAT to use ULA internally. You just use ULA for internal stuff and global addresses for everything else. But really, if renumbering is a problem in the first place, you are doing something fundamentally very wrong. Renumbering should be a matter of adding a new prefix of the same length to your addressing plan and replicating in it the exact same subnet structure you had before, then deprecating the old prefix (so it's not used for new outbound connections), waiting a bit, and then removing the old prefix. If your problem is hard-coded addresses everywhere, that is also a problem with your system design. Almost all of your configuration should only contain host names, and your DNS should either use dynamic updates so that hosts register their current primary addresses with the DNS server, or some other mechanism that generates records from an addressing plan of sorts and a prefix. There should be very few places where you need to change addresses in order to switch prefixes.