I gotta say this is one of the coolest things I've heard in a while!

http://www.svniis.org/

This is start, but it doesn't go far enough for me. The current setup still needs an Apache server running. The author is planning on hacking WebDAV directly, if there is enough interest. I would definitely love being able to get rid of Apache altogether. That's why I run my Subversion servers with svnserve.exe