A very quick mockup was made at
http://sage.math.washington.edu:8088/ http://sage.math.washington.edu/home/robertwb/databases/
The basis premise is that the "database" should be grown first by collecting a bunch of data, then it will be more obvious how to organize and present it. The pages above allow browsing and creating data sets (which are simply directories in the filesystem), and editing metadata about them online. This loose structure should be enough to start aggregating lots of tables.
Some discussion happened at
http://groups.google.com/group/frg-lm/browse_thread/thread/8140bbf3e95ce6bb?hl=en