* getting IPv6 provider-independent space is too hard
* extension headers are tricky, slow to parse, a source of tricky security issues, and thus are almost completely unused on the Internet in general
Basically almost all the moving parts in ipv6 (beyond the wire format and its 128-bit addresses) that aren't dangerously convoluted / mostly unused are pretty much just NIH'd reimplementations of the corresponding IPv4 protocols (like ARP, say).
Provider-independent space ought to be impossible - addresses should be addresses. If you want multiple routing paths to you, get an AS number and participate in actual global routing. Otherwise, accept that when you move your address will change.
TL;DR:
* Multicast and mobility are shits
* NDP an overcomplicated shit
* The SLAAC / DCHPv6 thing is a ripe mess
* getting IPv6 provider-independent space is too hard
* extension headers are tricky, slow to parse, a source of tricky security issues, and thus are almost completely unused on the Internet in general
Basically almost all the moving parts in ipv6 (beyond the wire format and its 128-bit addresses) that aren't dangerously convoluted / mostly unused are pretty much just NIH'd reimplementations of the corresponding IPv4 protocols (like ARP, say).