There are so many ways IPv6 remains broken and too many of the people with influence can tend to say 'working as designed'.
I know that's controversial, so I'll enumerate my pain points:
-DHCPv6 DUID is a pain to 'pre-provision'. When any operating system or firmware instance dhcpv6 for the first time, it sends out something that you'll never know what it would be ahead of time. In 99% of cases, the DUID is a generated value at 'OS Install time' that is used only for that specific OS, and a reinstall or livecd boot will change it out completely. stateless boot, multi-boot systems and multi-stage booting (i.e. pxe -> os) cannot hold together a coherent identity because DHCPv6 is explicitly designed not to do that. Binding by MAC is considered 'evil', but it has been the strategy used for ages. I wouldn't mind so much if DUID was commonly implemented as a value retrieved from motherboard firmware tables, but no one is stepping up to drive that behavior in a spec visible to all parties.
No PXE/bootp boot. I believe they are trying to reinvent, from scratch the boot design from IPv4, and are nearing completion. I fear the extent to which the baby has been tossed out with the bathwater (i.e. 'root-path' was dropped and no one has pulled it into dhcpv6).
Some standards are missing the capability to operate in IPv6. I.e. IPMI hase some IPv4 specific portions of the standard without IPv6 capable equivalents.