There are still too many rough edges going V6 only though, like if I set my own DNS servers, will they resolve A records to NAT64 AAAA records? And how will the regular Windows sysadmin deal with registering DNS records?
DJB saw all this with crystal clarity almost twenty years ago:
http://cr.yp.to/djbdns/ipv6mess.html
Note that when he wrote this, NAT64 didn't even exist. NAT64 is basically standardization of "make IPv6 work the way DJB said it should".
It doesn't make sense to have NAT64 on every router, because NAT64 is stateful and needs to be properly engineered into a network. There are also alternatives like DS-Lite and MAP, with different design tradeoffs.
(And mandating NAT in routers would be a pretty radical departure from the current internet architecture).
When there was only IPv4 there was no reason for backwards compatibility. Caring about backwards compatability doesn't become radical simply because it becomes necessary.