Malte
I'd like to be a little more clever about it.
The reason for multiple files is to keep the CSS in the right place.
The trick would be to compile a master css from the appropriate files when necessary.
It would be easy to do this once Lee's work on template::head is complete. Hamilton is looking at completing this work.
The advantage is that you still get modularity and the system can consistently manage the files for you.
I think allowing editing of CSS files from the web interface is really a seperate feature from this since the end result is a file in the filesystem the rest of the features only need to know the location of the file and it should not matter where it came from. I'd also think most designers would rather upload a complete file than edit it in a web browser.