I looked at doing it about a year ago (before Lion) and it's a big project - the current implementation just uses FUSE, and a real IOKit driver has to be create

I looked at doing it about a year ago (before Lion) and it's a big project - the current implementation just uses FUSE, and a real IOKit driver has to be created or it'll never be bootable. On top of that, EFI support has to be implemented, and it's a completely different animal than the BIOS hooks that are used for the Windows version. With FDE support in Lion, and the level of polish that's already there in Apple's implementation, it really wouldn't be worth the level of effort involved to implement.