PS: I once got stiffed for $6500, so I put up a "client hasn't paid" notice on the (demo) website for my code. I later learned that the guy I was accusing of non-payment was very likely a stolen identity. Some guy from Eastern Europe was using many fake identities and scamming lots of developers. So I ended up:
1) out $6500
2) feeling dumb for getting cheated in the first place
3) feeling bad for having pseudo-publicly excoriated a likely innocent
I wish in retrospect that I had taken the higher ground, open-sourced the code and just moved on.
Because it reeks a bit of airing dirty laundry, similar to the guy who added a "my client John Smith hasn't paid his bill, so I'm uploading this message to his website which I still control, in order to publicly shame him" which we saw a few months back.
Don't get me wrong- I think he's totally within his rights to (publicly) exclude him from the license. And as a developer who's been stiffed before, I sympathize. I think the restraint he's shown so far in that README is noble, and I hope he gets some good PR (and thus new clients) out of this.