I don't understand copyright law, either.

In your opinion, would it be legal for you to fork Lamson at a version before the revocation clause was put in the license, then distribute the source with that license?

Sure, depending on what the license was previously. I'm pretty sure that's happened before (LibreOffice, maybe?).

It has been GPLv3 before.

https://github.com/zedshaw/lamson/commit/d259a669728a92a386f...

Are you sure he didn't block you because the avengers came out on May 4th?

"The Vengeful Public Licence" does have a ring to it, although "The Ghetto Public Licence" might be more apt.