Non-free languages are not allowed to participate in Cops and Robbers challenges. And that's a good thing. If you choose an obscure non-free language, no one will be able even to attempt solving it and you get a free uncracked cop. If you choose a non-free language that is reasonably widespread, it's giving an advantage to those robbers who have paid for the language, which isn't fair either. But unlike other standard loopholes, this one isn't actually preventing bad content, it just keeps the challenges fair.
However, a large part of the appeal of Cops and Robbers challenges (to me, anyway) is that they allow users to create interesting programming puzzles (oh hey, where have I seen that phrase before...) for other users, or solving those puzzles. Some non-free languages like Mathematica and MATLAB have quite a decent user base on PPCG, and it would certainly be nice to be able to challenge other users of the language with a nice puzzle in a Cops and Robbers challenge.
So my question is, should we allow non-competing cops in non-free programming languages? If these are cracked, the corresponding robber's answer would also be non-competing. This way we wouldn't have to exclude some interesting languages from the fun of CnR challenges, but could still keep things fair.