I find that hard to believe. That may be true for endpoints, but I'm talking about the network infrastructure in between. There, I believe that the vast differences in the protocols on higher level (autoconfiguration, link-local addresses, temporary addresses, Neighbor Discovery as part of ICMP6 instead of ARP, ICMP6 itself, and so on and so forth) are much, much more work to implement than dealing with new DNS records and APIs, and the new struct sockaddr variants.

My point is exactly that I have a strong suspicion that the longer addresses are not the problem for slow adoption, the different network protocols and semantics are.