What does “userland” mean in this context? Closed source linux distributions? Closed source apps? What?

The gpl is generally considered to stop at the process boundary. I don’t really understand what you could do with a bsd licensed coreutils you couldn’t do with a gpled coreutils. You could make closed source Linux software which called coreutils in a child process. But by most readings of the gpl, you can do that today.

I suppose a company could fork coreutils and make it closed source, keeping their special extra command line options for themselves. But … I guess I just don’t see the value in that. You can already do that with FreeBSD. Apple does exactly that today. And the sky hasn’t fallen. If anything, it would be a relief to many if Apple’s coreutils equivalents were more compatible with gnu coreutils, because then scripts would be more freely portable between Linux and macOS.