Sorry, this is just a fragment.
( Need to write something here about why Ftwalk never connected as a language or project. Then some lame excuses why I think it's still worth pursuing. )
I think there are three useful directions that we can move in:
Minimalist Ftwalk is library which implements a small subset of Ftwalk, specifically the file tree search expressions that are functionally equivalent to the awkward expressions of find(1).
The main function of the library would take a script (a string or pathname to a file containing a script) and a file tree search list, compile the script, and search the file tree(s), evaluating each file against the compiled script
FtBackup (not necessarily the name) would be a program written for the single and explicit purpose of performing efficient, automated backups by synchronized mirroring.