Ah I didn't see those so I'll have to take a look. The reason I thought it was very difficult and maybe even impossible was mostly because passing through to GO changes the behavior or Java to a point where it could cause some adverse affects in applications tuned or expecting it to work as the other JVMs work.
For many things that may be the case, but to my knowledge Java doesn't make any strict assumptions about garbage collection. You can get drastically different behavior just by passing different parameters to your JVM for instance.
As long as the Go garbage collection works, it shouldn't affect how the program runs. That's kind of the whole point of GC. Hell, you could write a toy VM with no garbage collection, and it would work fine until you blew your memory.
Still a cool project either way.