Thanks for the reply. I understand btrfs is a preview (in fact it took me a day and a half of blaming filesystem corruption before I decided to look at the fstab and see the issue), but since this box is basically just a play thing for me I figured it would be fun to try (and nice to have the care-free snapshotting).
I've successfully recovered the install using the live recovery mode off the centos disk (manually editing the fstab and commenting out the line that adds user_xattr in nethserver-samba-conf). I'm sure if I had been a bit more patient I could have figured out how to recover the mount in the system, but my system-related Linux-fu is sub par.
I'm not familiar with the system calls/modules involved in that (admittedly simple) file so I wouldn't know how to detect the filesystem. I appreciate the invitation to contribute but I'm a hardware coder and very quickly get out of my depth hacking at large projects with complicated modules and system calls. Researching it sounds fun, but I'm already starved for time on this little project.
Since it's getting attention I'll throw in a quick thank you. This is my first return to server distros since a brief dabble in UTM boxes ~10 years ago. Things have come a long way and nethserver will likely become my router once I'm done messing around (and switched back to XFS).