If it's just an installer check then people could just use the old installer versions and update afterward right? Or are they planning on stopping updates for unsupported hardware that already installed windows 11?
My guess is one of the upcoming major updates will either refuse to install, or will try to install and fail, if you try that route.
Something like that happened with a 2006-era laptop I have with Windows 10. It ran Windows 10 fine for several years, but finally one of the big updates decided it no longer liked some of the Vista-era drivers I was using. The update would try to install, fail, and roll back. And since Windows doesn't let you turn off or disable updates, a few days later it would try again only to fail in the exact same way.