That's not a great example. Maintaining a full fork of QNX would not be terribly complex compared to maintaining a full fork of Chromium. The latter targets standards which are moving and evolving. Nobody cares which version of POSIX QNX is compatible with. (Also, Chromium is much bigger)

I think a fork could have some maintainers. I'd be more worried about people wanting to put new features in than anything else.