I am not sure it doesn't make sense for them to just move over to JRuby and have them all focus their efforts their.
Yeah, jruby+truffle could be pretty amazing for ruby performance.
However, having multiple ruby implementations is great too, and they probably would rather keep working on an independent implementation that they have full control over, and whose goals may not align perfectly with that of other implementations.
As they pointed out in the interview - it's not a free meal i.e. one could expect high memory usage and slow start-up times.
For me the slow start-up and the JIT requiring ~50K/req for warm-up just ruin the whole experience in coding the app in Ruby I'd rather just use Elixir.
Another interesting project is IBM's OMR [0] - compared to JRuby there are no slow start-ups and weirdly, being still a dev. preview it can run Rails and its deps. without issues, even better than Rubinius stable.
50k requests seems excessive, are you sure about that? :) Of course it depends on the implementation particulars, and profile-guided optimization may help, but needing a couple thousand requests to warm up is not so bad for a web application server that will see 100x as many requests as that.
If we're very lucky, Substrate VM will be released at some point, solving the startup time issues (and I believe many of the JIT issues, though less clear on that): http://lafo.ssw.uni-linz.ac.at/papers/2013_JVMLanguageSummit...
The OMR project definitely looks interesting, but it doesn't seem to be actively developed (or perhaps the most recent commits are just not public yet). But if it works that well, then maybe there's no need, hah. Will have to try it out.
Ruby+OMR is developed in three pieces: 1) the language independent core, then 2) The language dependent portions (i.e., the VM, and what we call the 'glue')
The language independent core is here: https://github.com/eclipse/omr. It's under active development, :)
I'm actually working on Ruby 2.4 support right now (supremely not prime time, but if you're curious, the branch is here: https://github.com/mgaudet/ruby/tree/ruby_2_4_omr_preliminar...)