It was a fun experiment. To me, the end result was just awful, but the point of the video was the process, not the result. He was asking the vocalists to go way beyond their advertised service by not just singing but basically writing the lyric and melody. I'm surprised that they stepped up. That might raise some interesting copyright questions.

In a way, though, they were doing what top liners do in some pop songs. The producer plays them the rhythmic foundation of the song which they listen to through headphones and basically improvise lyrics in the hope that they hit on something catchy that sounds like a good hook, lyrically and melodically. When the producer hears something he likes, the rest of the lyric and melody are built around that, not necessarily making a whole lot of sense, or at least not saying a whole lot. There was some Swedish guy who generated hit after hit that way a while back.

Having said all this, I think Fiverr is a great idea if you use it the way that John does.