In response to comments, I've added a third proposal to
https://www.mediawiki.org/wiki/Requests_for_comment/Square_bounding_boxes
which minimally addresses the "square thumbnail of default size" issue
without trying to solve any broader issues. This adds a new "auto"
value for the existing "upright" option, which would get the upright
factor to the current aspect ratio of the image.
--scott