[_bxg1]

If only there were a license that made the original project open but allowed you to license derived works in whichever way was most appropriate...

[starbugs]

There are such open source licenses: LGPL and MPL for example. These, however, come with their own set of caveats.

[mattigames]

That's exactly what Ton is speaking against here, he doesn't want add-ons to have specific licenses but to share the same 'freedom' Blender has.