Hi WP -- I don't know enough about Flash development to answer, but a cursory Googling revealed no Flash-based WebDAV software. Any programming language or software platform which supports TCP/IP can implement a WebDAV client or server; the real question is which language/platform is ubiquitous enough to serve as a GUI for the WebDAV functionality of Moodle? This is the age old question for web developers. Do we go with a lowest common denominator GUI (a web browser and forms), or use something more fancy like Flash or Java, but which requires users to install more software beyond a browser? (A separate but similarly flavored question is: Must we use the same language/platform, i.e., PHP, for both Moodle and WebDAV servers?)
It sure would be nice to see an existing GUI for configuring WebDAV access control, versioning, etc. I'm currently evaluating Jakarta Slide in this regard. I don't have access to commercial products such as Xythos WFS, which very well may have a nice implementation of such a GUI. Anyone seen an implementation yet?
Addendum: Google for Xythos WFS and read the hits within the top ten entitled "Xythos WFS", which correspond to instructions for various universities' installations of Xythos.