I've thrown some very experimental initial work on such an extension into Subversion; trunk/extensions/FileSearch.
Sounds great, Rob! Unfortunately, I can't access SVN at the moment*, so I'll just have to take your word for it now...
* I keep getting "Forbidden. You were denied access because: Access denied by access control list." for the SVN Web interface, as well as for Meta and images on Wikipedia. I'll try again from home tonight.
add that index-text to some searchable index, or store it in the mysql
Maybe I'm missing something here, but why not just throw that "index-text" into the file's description field?
-- F.