I'm not the language guru that David is, but I not ready agree with him yet. While JRuby is showing good progress at creating a fast, stable Ruby implementation on top of a non-native VM, I don't think we've seen what a native, tuned VM for Ruby can really do. I'm also not sure we'll ever see Ruby's community turn away from their own VM (be it Rubinius or the 1.9 VM) for the 'standard implementation'. This doesn't mean that V8 is without value to the Ruby community though. Again, David Griswold:
Whether Ruby ends up on V8 or not, I'm guessing that some of V8 will end up in Ruby.