I don't believe un-open source is a concept that can exist under past versions of the GPL. If you read the GPL, it has no time limit on the license. And the contract also has no termination conditions except for one (which the people downloading/modifying the program control).
Therefore, it appears an old version GPL license is a neverending license without a way for the original person to end it. So no, he cannot open-source any of it, even his own original work. He can stop distributing it, but since he gave a license to others to distribute it, they can just distribute the original. And unless they break the one term of the license, he cannot stop that.
Clearly, this is where you run into the concept of the GPL. It was meant to ensure that original works of software would always be available to use and modify. "Always available" are the key words. He is out of luck.
The new GPL (v.3) appears to grant a license for the term of copyright. Not sure what that means. But, it also gives a license to someone you distribute the work to from the orignal copyright holder. To me, this means if you try to distribute a project with someone else's modifications, the person receiving the project gets a GPL license on those modifications, not your expensive license. Since the original work can also be distributed, essentially this means the whole thing can't be un-open-sourced.
Basically, the only thing I think he can do it make his own modifications, and release those for a fee. He cannot stop anyone from releasing the original or the original with others modifications.
Therefore, it appears an old version GPL license is a neverending license without a way for the original person to end it. So no, he cannot open-source any of it, even his own original work. He can stop distributing it, but since he gave a license to others to distribute it, they can just distribute the original. And unless they break the one term of the license, he cannot stop that.
Clearly, this is where you run into the concept of the GPL. It was meant to ensure that original works of software would always be available to use and modify. "Always available" are the key words. He is out of luck.
The new GPL (v.3) appears to grant a license for the term of copyright. Not sure what that means. But, it also gives a license to someone you distribute the work to from the orignal copyright holder. To me, this means if you try to distribute a project with someone else's modifications, the person receiving the project gets a GPL license on those modifications, not your expensive license. Since the original work can also be distributed, essentially this means the whole thing can't be un-open-sourced.
Basically, the only thing I think he can do it make his own modifications, and release those for a fee. He cannot stop anyone from releasing the original or the original with others modifications.