Ruby on.... jetty?

So I'm playing around with JRuby, and I think its really cool. The java community has really come a long way and created some great tools for doing enterprise deployments, why should the ruby community spend time backtracking and re-inventing the wheel? The JVM has become a proven execution environment and with an open byte-code standard its trivial to compile to it (well not trivial, but do0-able).

So with JRuby you can get the syntactial sugar of ruby with the heavy lifting of such java services and JMS, hibernate, and even servlet containers. Currently Ruby on Rails uses either WeBrick or Mongrel as their web server. Both are written in ruby and, well, slow. If there is one thing the java community has done a good job of the past few years its build fast and reliable servlet containers (just look at tomcat and jetty).

What I'm wondering is how hard would it be to replace mongrel/WeBrick with jetty in a JRuby on Rails app? Just think of the performance gain with Jetty's NIO engine?