Hi Mark,
That sounds interesting. I take it you're not using the compiler as such, just loading code from across the network?
Google provide their own Java API to the App Engine datastore, and provide JDO-compatible wrappers. There's another JSR-compliant interface to the memcache.
So something that allowed the compiler to use JDO rather than the file system might be a worthwhile idea?
Cheers,
John :^P