I agree that the uninstall tag is too broad. It's a big tag that currently has 2,262 questions.
I don't mind creating a new system-uninstall tag though. It would be another big tag. Searching for "Ubuntu install" questions returns 476 results. I don't see any reason why it wouldn't be possible to request in the tag wiki excerpt to restrict the system-uninstall tag to be used only for currently supported versions of Ubuntu and its officially supported flavors.