That isn't something Canonical could do just because the software has a permissive license instead of a copyleft license. They can do that if they own the copyr

That isn't something Canonical could do just because the software has a permissive license instead of a copyleft license. They can do that if they own the copyright (which I can't imagine they do), but if they own the copyright they can do anything they want and nobody has a say in it. So again it has nothing to do with license. The absolute most that Canonical can do is start making a fork of the software where they don't distribute the source code. But in that case, the original code is still right there. No freedom is lost at any point.