For those of you with this handy technology, the mobile phone, in the United States: you have an IPv6 address without NAT. Some of you even exist on a network using 464XLAT to tunnel IPv4 in IPV6, because it's a pure IPV6 network (T-Mobile). These mobile phone providers do not let the gazillion consumer smartphones act as servers for obvious reasons.

This is all to underscore the author's point: NAT may necessitate stateful tracking, but firewalls without translation has been deployed at massive scale for one of the most numerous types of device in existence.