Good that most/all the fuse filesystems are open source so you can benefit from them. An interesting project, but why not open source the amiga library too?
Not everyone wants to release their stuff as open-source. Not all OS4 things are open-source for easy porting to MOS either. I think it'd be disappointing for MOS, OS4, AROS to all be nothing more than open-source ports of each other, and thus really nothing more than all being a port of Linux. It's nice to see something unique in each, and having the others see something interesting to do their own spin on.
Now, Fuse itself is part GPL and part LGPL, I'm not sure which part the amiga library of Filesysbox would be modeled after. I'm not sure how "clean" he did his implementation. If it's only hium, someone could perhaps harass him about licensing. If there's a spec doc or someone else created one, and he did not need to look at (L)GPL code at all, then he should have no licensing problems from anyone.
Now, I think this is a cool idea. I've also pondered wrappers to Linux network and other driver APIs, but have no time to actually do anything. I'd like to see an equivalent of this FUSE thing for OS4 etc.