I agree with Gorka, this would be a good GSoC project. But there are other ways to mount the device. Have you tried u9fs (http://plan9.bell-labs.com/magic/man2html/4/u9fs)? Or drawterm from a Mac with the drive connected? Or running Inferno hosted on the Mac and exporting the volume?
Any of these would make the HFSX file system available to your Plan 9 host. -jas
