Having to audit every commit in what was a FOSS project to make sure the parts I care about weren't relicensed out from under me sounds like a lot of work.
I use Emacs. If the FSF suddenly started pulling parts of it out, I would not sit there and hope that they didn't come after the bits I need. If someone forked it with strong assurances that I could keep using all of Emacs, I'd probably switch to that work. "Just fork the bits that get taken away" would not be an option I'd consider.
