I think the majority opinion, judging by the likes of gitlab, is to use some or a lot of open source to entice people to pay you for plain ol' proprietary software. Closed shell, or open core.
It looks like there's only room for one RedHat in the world, only one company who truly sells free software. As I understand it, you can pay Red Hat for access to their repos, which provide free software with source code, and nothing else. They really do plainly sell free software, but I think they call it "self-supported" or similar.
edit: I'm of course aware that RH sells support. I just don't know any other company that plainly sells free software like RH also does. I wonder why no one else even tries.