Further progress on the Java front. Kaffe OpenVM 1.1.3 now runs all tests (which includes being able to run Jython) for my remote object protocol library TwistedJava . Kinda slow since there is no PowerPC JIT, but I suspect that has to do with the startup process and Jython's importing system, the actual tests are pretty speedy.
Hm, maybe I should rephrase. I didn't make any changes to my code, rather Kaffe has been improving. So now there are two open source Java implementations that are good enough to run my code, which was written for the standard Sun JDK.