As long as it's not the only *nix implementation of note there's no problem.
I can graph Linux adoption and project an inaccurate date in the future when there will be no notable other *nix implementations. Whether everything will continue to be as okay as it is now is debatable; I'd say that we've already reached "only one notable implementation" land when it comes to certain categories of use. It will get worse and I just hope that nothing really bad happens as a result.