I would recommend looking at some of the ideas that ReiserFS was trying to do -- and some of the ideas about metadata and expanding some of the concepts of file

I would recommend looking at some of the ideas that ReiserFS was trying to do -- and some of the ideas about metadata and expanding some of the concepts of filesystems were present in their ideas as well. In particular one idea they had was allowing you to do things like SQL searches in your filesystem, using filesystem plugins (effectively the idea is to allow for database structures to be stored using filesystem plugins so that searches and operations become just VFS operations). Obviously we know what happened to Hans Reiser, but I've always felt that some of the clever ideas in reiser4 were not fully explored because of what happened.