On the contrary, having IPv6 only sites and protocols would greatly help adoption. One of the problems is that a lot of companies think that IPv4 is good enoug

On the contrary, having IPv6 only sites and protocols would greatly help adoption. One of the problems is that a lot of companies think that IPv4 is good enough, since there's no discernable difference to end users right now. Every IPv6 site is also accessible over IPv4, and the community is already heavily invested in engineering around the shortcomings otherwise created by NAT on IPv4. Coupled with the additional cost and security considerations that have to go into an IPv6 deployment, we've got a good recipe for encouraging both ISPs and corporate providers to stay on IPv4 for as long as possible. (If we're unlucky, we might even see ISPs roll out carrier grade NAT instead of upgrading.)