I really admire the work of Charles et. al. and we have a couple of Rails apps on top of Jruby in production. Unfortunately, while the language implementation is itself is developed constantly, the ecosystem has stalled.

The activercord jdbc driver implementation is particularly problematic because it effectively keeps us from upgrading to Rails 5 (we use SQL Server as backend). There is also a lack of app server options. The Jruby app servers like Trinidad or Torquebox are not maintained. Warbler has issues, too.

Charles and the other devs can, of course, spend their time however they want, but from my perspective, having a well maintained software stack for production deployments is far more important than a further speed optimization.