I know this has been discussed elsewhere before but still it is not clear to me.
I am currently investigating how to publish a freemium plugin:
The free edition is a fully functional plugin, that I intend to host at wordpress.org and license under GPLv3. All of the code and assets is my own work except for a library I include which is distributed under the Apache License 2. (I read somewhere that GPLv2 is not compatible with Apache 2, hence GPLv3 it is.)
The premium edition of my plugin includes all the code from the free plugin, plus some extra features. I would like to not have to split my plugin into two unless I absolutely have to.
I have read the wordpress.org guidelines and "upselling" is clearly allowed. However I do not understand what the license of my premium edition of the plugin would have to be.
Does the premium version need to be dual-licensed? i.e. GPL + something proprietary?
Does that mean that users who buy the premium edition will have the right to redistribute my premium code? And if so, do I need to worry about this in practice, or is software piracy rare in the WordPress world, as others have suggested?