What's wrong with IPv6? The only complaints I've seen are "the numbers are bigger", as if that's not the point, and that makes them harder to remember.
[0] https://social.technet.microsoft.com/Forums/windows/en-US/57...
So people who have been trusting NAT to be a firewall wake up one day to their network being directly routable, and are none the wiser.
Most endpoints these days don't have much if anything listening by default though. The reality is that even trusted local networks are hostile networks, and vendors have responded to that.