I also have my doubts. Take an eaxmple of a library we recently purchased at our company. It is open-source, free for personal use, paid for commercial use. Other than the licence terms, there is no difference between the free and the paid version.

So far so good.

I may be wrong but I think Copernicus was considering a different model. A free version with limitations, unlock full features by buying an activation code. I am not sure how this model would work if anyone could access tbe code and see how it works and how to modify it to bypass the activation.