If it is only code you wrote and you haven't transfered your copyright to the project, then No, this creates no standing.
> That's what's so new about this. There is now a contract (not copyright) element - which binds you and the recipients of your code.
Incorrect, there is a contract that binds you and recipients of the code under a GPL license.
If you receive that code under a different license, that contract doesn't exist.
Edit: Let me put it this way. Let's say you create a library and make it available under GPL. Any company that uses your code under that GPL license, has entered a contract with you that allows users of their software to sue them for GPL violations. However, you can also simultaneously offer a non-GPL, proprietary license for that library to paying customers. Those paying customers would not be part of any GPL contract, they would instead have whatever contract they signed with you when buying the proprietary license. The users of that paying customer would have no grounds to sue that paying customer, because that paying customer never agreed to the GPL contract. (OFC if you use other people's code in your library under a GPL license, then you don't have the legal right to offer a propriety license for that code.)