Sure, everything supports IPv6 -- until you turn it on and rediscover the tickets that have been sitting at the bottom of the JIRA for the last decade.
As a matter of fact Ron Broersma who affiliated with Space and Naval Warfare Systems Command (SPAWAR) has a list of equipment that should be fully IPv6-only compliant including various management interfaces and more. The US Navy supposedly tests this in house in a IPv6-only network. 4 years later I imagine the situation only got better https://www.youtube.com/watch?v=9kQje5gSWw8
Also, AWS now have the majority of NICs and switches built in-house I imagine. The underlay network could be IPv6 or totally custom for what we know (but probably is IPv4).
Cool! I'm glad the military is pushing the internet forward, I guess some things never change :)
As for AWS, I tend to agree with the sibling post and your supposition about IPv4. Everything out of the Amazon organization is aggressively, err, "minimal."
Also, AWS now have the majority of NICs and switches built in-house I imagine. The underlay network could be IPv6 or totally custom for what we know (but probably is IPv4).