We welcome GAE users of JRuby but they never seemed to be a big segment of the community. And we continue to maintain non-native IO and process logic for limited environments. If that is not sufficient for GAE, we'll work with you to make it so.
Jruby 1.7 simply doesn't work in GAE, and maybe it's not worth making it work there, which I would understand. I opened an issue a while ago (https://github.com/jruby/jruby/issues/2304) and I spent about a week trying to fix it. Each time I fixed one issue another one popped up and I gave up after hacking up JRuby beyond my comfort level.
Edit: I just want to stress, the JRuby team is amazing, and I've always been impressed with the responsiveness and openness of the team. This comment isn't meant as a critique in anyway, just a statement of fact with my experience trying to run JRuby on app engine.
