<quote who="Erik Moeller" date="Sun, Dec 02, 2007 at 01:12:09AM +0100">
We could, for a transitional phase, allow photographers to change license templates on media they hold the copyright to from an (arguably or not) permissive copyleft license, to an explicitly strong copyleft license. This would not invalidate the old templates, but at least ensure that people finding the files on our site would be asked to respect the strong copyleft provision.
After the transitional phase, strong copyleft would just be a choice for new uploads.
This all presumes the existence of a strong copyleft license in the first place. :-)
This sounds like something WMF should pursue with CC now, while the foundation has leverage.
Regards, Mako