Really? The network protocol someone uses is so critical that it should be illegal to use the wrong one? What happens when IPv9 becomes the hot new thing, but everyone is stuck on IPv6, because of some outdated government regulation? Do Americans have the right to use whatever internet protocol they want, under the first amendment?

IPv6 has made enough progress that it's totally possible to run your network off of it, regardless of what everyone else is doing, and if all of your neghbors are using IPv4, it won't harm your IPv6 network.

Also, part of the delay in the switch to IPv6 is that some work is needed to ensure that home routers and IoT devices default to reasonable security settings, and the absolute worst thing to do is force them to switch first, and figure out security later.

The answer isn't to force everyone to use something before its ready; the answer is to address every impediment, so it's worth it for everyone to switch. Sure it's slower, but it's much better than making users worse off by switching, converting them to detractors instead of supporters.

I don't see a reason why IPv9 would ever need to be a thing.