There is some merit to having more IPv4 space e.g. for new players trying to start a business or for IPv6 transition technologies, where you need at least some

There is some merit to having more IPv4 space e.g. for new players trying to start a business or for IPv6 transition technologies, where you need at least some IPv4 space e.g. for the NAT64 gateway. This should be considered in the application process for the space, if the unicast extension will be widely supported technically. The real question here is, whether Microsoft will patch Windows to support the unicast extension. More specifically, which versions and whether it will include Windows XP/ Windows Server 2003/ 7/ Windows Server 2008 and various Windows CE versions. I would say, there are so many WinXP/WS2003 machines in industrial networks still, that not having a patch enabling support might be a major blocker. In some cases, you just cannot replace the operating system without also replacing the machine it is driving. Yes, more or cheaper IPv4 space will prolong the pain of having two protocols one of which is the default but has inherent problems in terms of scalability (IPv4). There might also be some damage from changing 0/8 and 127/8 to be global unicast and carving out 0.0.0.0/32 and 127.0/16 for their current usage. Also the lower address as alternative broadcast to unicast switchover could be "fun" in some networks. The reality is, ransomware and other attacks are quite common and creating new doors into legacy networks with less than ideal maintenance through changing rules should be evaluated. I don't think the typical water treatment plant, hospital, pharmacy or an aluminum smelter follow even major RFCs closely. I know, I have discovered (and fixed) the 1/8 blackhole problem in a subsidiary at my previous job. I would need to really check 0/8 and 127/8 there to verify they are ready for the unicast extension as well. That company had an IT department and the IT worked reasonably well there but there were some very specific constraints such as Windows NT driving some industrial machines. This wasn't the common case, but it wasn't the only "special" host on the network. In such places, such changes perhaps don't need to be implemented, but you never know, when the inconsistency will bite you.