That certainly isn’t my goal! JRuby would always be an alternative, and in some cases it may be a better choice than MRI for larger deployments. A single JRuby instance can handle an entire server load, maxing out all cores. If you are getting to the point of running 3 or 4 or 5 MRI instances, there may be a good case to try JRuby.
We also usually perform better, but that may take some tweaking early on.