Interesting question, but IMHO a rather crap analysis. They don't seem to make any distinction between completely separate legal issues.
For example, I'm sure the DoD could classify some software that was a derivative work of some GPL licensed work as top secret. IANAL buy my guess is that the classification itself would probably be upheld by a court, but that wouldn't bring the DoD into compliance with the GPL. I cannot imagine that. It would be a complete carte blanche for the DoD in regards to any and all IPR. Even if they could legally do it I cannot imagine them doing it. It would be outright theft.
The same goes for modifying the GPL. I can go and rip off the GPL and license my software under the "Bjornsing GPL Derivative License" all I want. If somebody licenses my software under those terms they are no less bound by the license just because I stole the license itself. That's a separate issue between me and the FSF (and possibly between me and the state if deemed criminal copyright infringement). At least so I imagine. Again IANAL.
While you can certainly license your works under "Bjornsing GPL Derivative License" if you want. The point being made (by the FSF) is that your license would probably be incompatible with the GPL itself, thus your code could not be legally linked against any piece of GPL code, effectively separating it from that ecosystem.
For example, I'm sure the DoD could classify some software that was a derivative work of some GPL licensed work as top secret. IANAL buy my guess is that the classification itself would probably be upheld by a court, but that wouldn't bring the DoD into compliance with the GPL. I cannot imagine that. It would be a complete carte blanche for the DoD in regards to any and all IPR. Even if they could legally do it I cannot imagine them doing it. It would be outright theft.
The same goes for modifying the GPL. I can go and rip off the GPL and license my software under the "Bjornsing GPL Derivative License" all I want. If somebody licenses my software under those terms they are no less bound by the license just because I stole the license itself. That's a separate issue between me and the FSF (and possibly between me and the state if deemed criminal copyright infringement). At least so I imagine. Again IANAL.