There are proper ways to do that, changing the license in a next version for example is how I think it should have been done in the first place. I've said it before here but this has all the markings of being extremely petty and Mullenweg not happy with their own licensing model.
Can Matt do that though? I don't _think_ WordPress has a copyright assignment agreement for contributors? So neither Matt nor Automattic nor wordpress.org nor The WordPress Foundation can choose to re-license future versions of the GPL2 or newer codebase without agreement from _all_ the contributors who retain the copyright in their part of the code.
This self-described war he’s going on is all about commercial trademarks, and other hosting companies having more commercial success than Automattic in the ecosystem while contributing fewer developers and less money to the project.
Now, he’s taken it to a very extreme extent, and I fully disagree with his approach, but the core issues (for him) have nothing to do with GPL and how the WP project is governed. Those has even the same for decades, and he’s not trying to change them.
He’s just being very self-destructed because it turns out the community has no interest in some kind of “war” that gets long term contributors locked out of the ecosystem. He was expecting more people to be on his side, and frankly now seems to be lashing out (by blocking people) when that didn’t happen
None of that means he’s trying to change the governance model or license.
I don't really buy that, there is no obligation for anyone to contribute to the project at all under the GPL license so he can feel whatever he want's about it but it's irrelevant.
Also as for the trademark issue, in an older version of their trademark stated "The abbreviation “WP” is not covered by the WordPress trademarks, meaning people may use as they see fit. "
You can't retroactively change it once you see other people making more money than you. That's not how trademarks work.