I remember the time that widescreen was a novelty, and even Windows games had problems dealing with it. But was just a matter of upgrading the video drivers to resolve the problem.
I don't know if there is a solution for Linux and Mac in this case. I've tested your game in my PC, which have the Nvidia proprietary drivers installed, and in my notebook, which only have the open source drivers. In both it runs the same way: stretched picture and no controller. That's a shame.
Anyways, thanks for the attention, for the answer and for this awesome demo! I will be waiting for the full release! :D