OS X El Capitan has been released, and my iTunes Play Button Patch is not compatible with it because of the new System Integrity Protection (SIP) that restricts any user (even root user) from modifying any system files. You can get around this by temporarily disabling SIP, applying the patch and then re-enabling SIP. I feel like this is not a good solution because it is cumbersome and it will likely have to be redone every time iTunes is updated (something needed by the existing method as well).
So, what’s the alternative? I have used Vox music player on and off, and I noticed that it has a preference pane which works with El Capitan and accomplishes the same goal with a different approach. I believe they use a background service that listens for the key and handles it, if configured. I feel like that’s a better approach to this problem and properly deals with the SIP restrictions that Apple has added to OS X El Capitan.
I am new to OS X service programming so I am going to research and see if I can learn about it to address this need. This will likely also address the enhancement request that many folks have submitted to allow control from other devices.