The real issue here is running out of IPv4s.
We don't really need more IPs for clients - NAT fixes that problem (I just argue that SOCKS could be a better solution, that can work alongside NAT).
We need more IPs for servers. The IPv6 solution is to move clients and servers to IPv6. 6in4 gets around needing to migrate the ISP as well, which is good, but it's still a heap of work that has to be done by people who don't get any material benefit out of it for years, at best. So it won't happen.