After reading this I think the only sane thing to do is to trash dos.library + FFS and use emulation for legacy filesystems. I can't come up with a single reason for sticking with FFS or the weird DOS in the future.
I'm using SFS (SmartFileSystem) now and I've never looked back. If dos.library is everything that stands between the users and even better filesystems, then there's not much choice as far as I'm concerned.
To hell with FFS and re-implement dos.library instead. Let's migrate people. Backwards compatibility at any cost is not a virtue.