Every plugin creator has the right to choose whichever licence they want their plugin to be published under. That is clearly indicated in the plugin.yml file.
The question is not weather the published content can be copied or not, the content no matter if it falls under copyright or not CANNOT be copied unless explicitly said that it can be. Copying content that is not explicitly published to be copied is in the best case plagiarism, and in the worst case copyright infringement both of which are crimes at least in Europe and the latter at least in the USA too. As posted above after the incentive @Miwarre gave me to look for it, in Europe it is technically even illegal to decompile the code without the explicit permission of the person who wrote it.
I am expressing an opinion that authors refrain from publishing in free access area if they are worried about people copying or modifying their free published software plug in and not a legal one at that. Why don't we use this thread to teach rather than yelling at one another? I think the EU rules are really clear about personal rights by legal owners of software they own. You need to be really careful before you start yelling that a decompile is illegal by the anyone that got it off a free download site unless you send with it in the file license agreement that is a specific means for a change in these rules. This could require a Qualified Person or person of knowledge if this needs to go to court.
It is my understanding that there is not a plugin-in published or distributed in violation we are talking about. If so it probably needs to be removed from the board and handled by JIW legal?
My opinion expressed was that the EU does allow "copyleft" in the EU and tons of of EU programmers use that everyday even in commercial items for commercial purposes as long as they put the same license in their routines. JIW, clearly as I linked in my post, claims EU rules and therefore, DIRECTIVE 2009/24/EC would apply. Having certain rights transferred and clarified for posting plug ins would make life easier for them and those that want to "stand on the shoulders of giants" so to speak and create a really nice game here.
Having said that, I would advise that everyone read DIRECTIVE 2009/24/EC Article 5 and 6 decompilation that the program users have certain rights for decompile for interoperability and errors correction in having a license to have a copy and use it. In particular Article 5 paragraph 1. In the absence of specific contractual provisions, the actsreferred to in points (a) and (b) of Article 4(1) shall not requireauthorisation by the rightholder where they are necessary forthe use of the computer program by the lawful acquirer inaccordance with its intended purpose, including for errorcorrection.
link to EU directive in all languages.
https://eur-lex.europa.eu/lega…=CELEX:32009L0024&from=EN