Not really. It has to be possible in practise to make proprietary modifications, get them accepted into common use, somehow prevent other people just cloning th

Not really. It has to be possible in practise to make proprietary modifications, get them accepted into common use, somehow prevent other people just cloning them, and steal the momentum of the open source project. If someone makes proprietary extensions to "ls", they are just going to be stuck maintaining a fork. There is no realistic threat here.