Iot isn't what's holding ipv6 back. There are tons of websites and even cloud platforms with totally ipv6-capable hardware and OSes, but the services are v4-only or strongly v4-preferred.
IPv6-lacking hardware and software definitely do exist in the wild, have you seen how some programs from incompetent developers accept only IPv4 addresses in the config files? I think all of us have seen at least one such program.
Often times it's just a matter of using another function to parse the address string. But you are shit outta luck if the program is closed source.
IoT was an example, a glaring one at that.
IPv6-lacking hardware and software definitely do exist in the wild, have you seen how some programs from incompetent developers accept only IPv4 addresses in the config files? I think all of us have seen at least one such program.
Often times it's just a matter of using another function to parse the address string. But you are shit outta luck if the program is closed source.