Grsecurity did the same thing with their kernel patch. Used to be GPL. Now it's GPL+N(o redistribution).
>But you can't do that if it's not an original work
They did.
RMS completely agrees that you can make a patch of the linux kernel and GCC and distribute it under any license you want.
(See image attached)
It can be completely proprietary if you want.
Ask him about it at rms@gnu.org