I don’t want to start another debate on the same topic. What I do want to do is come up with a way to guarantee that plugins adhere to the GPL by forcing them to do so with the architecture of the plugin system.
One idea that I had was to somehow force plugins to copy code from the parent program into the plugin itself in order for it to work. On the simplest level, this could be something like a driver type of file that the parent program checks for the existence of, and which contains base classes or something similar that must be extended in order for the plugin to properly hook into the main program.
I have not thought this through completely, so please post your feedback or your own ideas.