Hi,
IMHO the function that is missing the most in api.php is image properties (width, height, size, media type, etc); the equivalent of imageinfo on query.php.
When this is added, it might be nice to get information about the thumbnail name as well, with a placeholder for the thumbnail width.
Also, one might want to think of making "file" an equivalent to "image", so that "image" can be abolished later. Finding oggs in your "image" list can be quite surprising otherwise :-)
So far my list of demands to be solved today ;-)
Cheers, Magnus