If someone wanted to maintain the PKGBUILD for this project, it’d be trivial to include a patch that removes the code he added trying to make it not build.

Or, to make sure to not be in breach of the no-derivatives part of his lisence, just reimplement it and ship with a patch that fixes his “blocker”.

I wonder if he received permission from all the other contributors to change the license of their contributions.

You have absolutely no idea what you are talking about, but hey!

https://en.wikipedia.org/wiki/Lutefisk