moodle.org (and especially moodle.org/plugins) is a place where PHP code is uploaded often - either as a ZIP package or forum attachment etc. It sounds silly that the GNU/GPL license can't be chosen for uploaded files - given that the mark in the footer clearly says that all the content on this site is expected to be GNU/GPL'ed. So my suggestion is to

• Add "GNU General Public License" as a new available license for the file picker.
• Make it default for all files.