All rubinius really needs is a non-overlapping set of bugs with MRI and JRuby. That would give it a niche to springboard from. I've been hammering all three with a project which is heavily threaded, and heavily socketed. These are both classic problem areas for MRI, and I've been cranking out JRuby bug reports as well. If rubinius got it right, then we'd be using it instead, but it's not quite there yet.
