I would like to have he exif date of a photo rather than the file date that's
produced by the system.

The reason is this:
When I reupload a series of older photos, all taken at different days they all
have the upload date set by Gallery/the file system. So it's not really possible
to sort them. As php has a function to read the exif data it should be possible
to implement this into Gallery. ( maybe as an additional option?)