It's an interesting idea, but the differences between copyright and contract law present quite a hurdle.
Either you release something publicly, licensing it under certain conditions (you can use it this way, but not that), or you cut a contract with a 3rd party for them to use it a certain way -- something that only makes sense in a context where the wider public doesn't already have those rights, otherwise a contract would be unnecessary.
You see it in some Free software projects: they're licensed under something aggressive like the AGPL, but for a few you can buy a proprietary license. This of course limits community participation though, as to contribute, you must agree to these terms. I think React does something like this, forcing you to sign a contract to submit a patch.
He points out a number of problems that I'd like to see solved, so I'd love to hear his ideas, so long as they're similar in spirit to the goals of the FSF.