As far as I can tell, IPv6 is at least theoretically capable of
offering exactly two things that IPv4 does not offer and can't easily
be made to offer:
1. More addresses.
2. Provider independent addresses
At the customer level, #1 has been thoroughly mitigated by NAT,
eliminating demand. Indeed, the lack of IPv6 NAT creates a
negative demand: folks used to NAT don't want to give it up.
This community (network operators) has refused to permit #2,
even to the extent that its present in IPv4, eliminating that source
of demand as well.