Hi Grant,
I can answer the "is there an easy way to integrate said filesystem into musllibc such that one could use the
standard open/read/write/close functions"?
The answer is yes ;). Take a look at libsel4camkes [1] which already binds some of the common C library functions. You could extend these for some subset of file descriptors that identifies your file system, or base an implementation on the code in this
library.
[1] https://github.com/seL4/camkes-tool/blob/master/libsel4camkes/src/sys_io.c
Cheers,
Anna.