Sorry to short-circuit the process to add functionality but this one is an essential. And I clearly feel its lack when I tested T1884: TAB + any key doesn't work.
At the moment, the only way to reset options to default is to go straightly delete files in game directory and know what to delete. So it's not a good way.
The files named "settings.cfg", "keyboard.cfg", "joystick.cfg" should be easely resetable from the option menu in GUI by pressing a simple "DEFAULT" button. It'll be user friendly and avoid to have to close and restart game each time we have to test issue with keys binding.