After searching for the official specification (a term used formally in the license), the only thing I could find is the web page for the documentation that is called the official shen standard doc,
http://www.shenlanguage.org/learn-shen/shendoc.htm, so I suppose the official specification is the content of this page. As I don't have the book of Shen I can't tell if there is further documentation about the "specification of the language".
The author in the license page claims that he is not going to make a fork illegal by changing the standard in such a way as to make the fork retrospectively illegal.
There was one author who made a close source port of Shen in java but then there were big problems. Perhaps he could give a lot of information of what kind of problems are you to encounter when you try to develop a close source product using Shen. The last think I can remember was that he bought the book of Shen for her 16 years old daughter and he was emotionally very interested in Shen but then all went down. [By the way, I apologize for not putting the 's i the third person )). in my other posts.