They have permission as long as they comply with the license (GNU GPL v3+) and the author can't revoke a license already granted unless the license allows to do

They have permission as long as they comply with the license (GNU GPL v3+) and the author can't revoke a license already granted unless the license allows to do so, and the GPL doesn't allow it. See: "The Non-Revocable GPL" http://www.groklaw.net/article.php?story=2006062204552163 http://www.groklaw.net/article.php?story=2006062204552163