Reading from GPL code is bad for our firmware. We can't be tainted by stuff like that in certain parts of R&D
Documentation would be best, we can get by with a simple on-disk format, like you can get for XFS or ZFS or other filesystems.
Can the current RISCOS read FAT fairly reliably? I would assume so, in which case, there is probably not going to be much trouble having a boot partition of FAT format containing ROM files and other boot-time support, and then the rest of the OS inside another partition..