[magnawave]

Indeed vary brave. Filesystems ARE NOT and never have been an API to exchange data between multiple OSes - they are a means to persist data efficiently for a single OS. Now if you don't mind breaking a bunch of the FS rules, sure compatibility hacks can always be written - but are you really sure each implementation is FULLY honoring the rules. I can guarantee you, for anything but the simplest filesystems, the answer will be "no". Hell, even FAT has implementation stragglers out there in the wild and its brain dead simple.

Use an API for cross platform sharing layered on top of a filesystem: Either a Virtual Machine sharing protocol (aka 9p virtio) or a real network protocol AFP/SMB/NFS. Anything else is taking your data in your own hands and is antithetical to the design of modern OSes.