This content of this page has been updated and migrated to the new Moodle Developer Resources. The information contained on the page should no longer be seen up-to-date.
There is a Subplugins structure for building default database presets in Moodle.
These are located under /mod/data/preset and the format should be easy to determine from the one example that we have there, called "imagegallery".
It's unlikely we'll add more, though. The main way to share presets is to import them on the fly as .zip files.