If I take GPL code and release it under a non-compliant license, I can call it anything I want, but it is still GPL per se.

No, it isn’t. I cannot take code and violate its license just because I disagree with it or because I don’t think, believe or know it to be incorrect or inaccurate. I am still bound by the license I agree to when I download or use the software.

But let’s support I know software to be in violation of the GPL, then my only lawful recourse is to take legal action of some kind to seek remedy. For me, that would start with me hiring a lawyer to write a letter saying in essence, “you are in violation of the GPL and here is why; change your product or we will bring charges against you.” In some cases a strongly worded letter and a threat of a lawsuit will be enough to obtain the remedy you seek. Alternatively the software publisher may in turn say, “I disagree. I believe I am in full compliance with the GPL and I will see you in court.”

Let’s suppose I take a different course of action. Let’s say that I turn vigilante and decide to blatantly disregard the license because I believe it should be GPL (even though it is not explicitly). I distribute my own derivative work based upon the software. All fine and good I suppose. But then let’s say down the road it is determined that the software is completely within its rights to not be GPL. Now I am liable for damages/lost revenue to the original copyright holder because I willfully violated their license at the time.

The point is that whenever you choose to disobey a software’s explicit license, you become liable in some way. Even if you feel justified in your action it ultimately is not up to you to determine what is legal and illegal vis-a-vis that software.

In other words: I can’t say that a theme I designed is anything other than GPL without breaking the license of the product (ie WordPress) I’m using. I’m pretty sure we agree on that.

Actually, no, I don’t think we necessarily agree on that. My point is that the definition of “derivative works” as it relates to “dynamic linking” is a hotly contested topic. People with significant pedigree exist on both sides of the argument, and I bet if you dig a little deeper for this particular argument, you will find the same: convincing arguments that will support both claims: that WordPress themes are free to license themselves under a proprietary license, and that WordPress themes must be GPL.

I wonder when we’ll see the first court case concerning a WordPress theme or plugin… Hopefully never, but you never know.

There is nothing about the GPL that enables it to forcibly change the license of another piece of software. The only person who can do that is the copyright holder. Period.

So what does this mean? Well, it means that the WordPress Foundation has reasonable cause to ask each theme designer to:

a) change their license, or
b) cease distribution of their theme.

If the theme designer refuses, the WordPress Foundation can seek a court order to force the user to cease distribution, or in some other way come into compliance with the GPL.

Orthogonal to that, the WordPress Foundation also has reasonable cause to seek damages from each theme designer if they can prove they lost revenue or some other quantifiable sum of money while the theme designer’s software was not compliant with the GPL.

It is hard to solve this since WordPress is GPL and the only way to get away from GPL is to redo the whole thing in another license, like LGPL or similar.

I wonder how this will affect plugins since a similar argument can be made. There’s plenty of paid ones like OIO Publisher, Ninja Affiliate, or WP e-Commerce Gold that don’t have much CSS/images to distinguish themselves from a gratis GPL version. I wonder how they’d fare.

Here’s hoping that the WordPress team works on looser coupling so that non-GPL themes can be made.