All premium theme developers (including myself) are not actually selling the theme if they use GPL licensing, but they are selling support and upgrades. So, distributing pirated themes is affecting only users that use such themes (malicious code they usually contain and no support). With GPL you can't really stop redistribution and you depend on the users honesty not to pass on what they payed for.

If a premium developer sells a theme and then not provide support for the themes, than it would be a good thing to have some way to 'report' such developer and warn other users to stay away. WPTavern forum is a good place to start, and maybe you should add a section or thread fur such discussion.

WP.org should be used for free themes that are available in repository, there should be a general area for questions about WP specific stuff that affects any theme (including premium) and that's it. No help decoding the encoded/malware themes should be there, we need a way to warn users about danger of using such theme obtained from websites of the questionable legality. All WP developers should try and raise the awareness of this problem and help users to avoid such websites. Helping them using such themes and remove malicious code is bad, bad practice and should not be allowed. Premium themes are more and more used (I think even more than free themes), and if WP.org starts to go against premium developers even with such 'small' changes to WP.org forums, it will alienate premium developers.