Has this been tested in court?
I also don't think "this is a license for anyone not the copyright holder" is accurate. The license specifically prohibits removal of the license you can't "dual license" GPL code.
You can license code under GPL, and you can license the same initial code under a second license, but going forward those two pieces of code are forked. You can't then ship GPL modifications to the other license simply because you have the copyright ownership of the modifications, well, in fact you can, but that requires the GPL license to infect the other source code. You being the sole developer in all of this is irrelevant.
I think this comes down to the answer of this question:
Can you rescind a GPL license?
If not, even as the copyright holder, then no, you as the copyright holder don't have rights over the code moving forward.
That was part of the purpose and intention behind this license.