I know it would be a very specific peripheral, but there are several manufacturers that create specific and high end devices for sim racing, and I think there would be many users interested in it. Besides, it wouldn't be too hard nor expensive to make. The kind of peripheral I'm referring to is a single flappy paddle gear shift, which installs on the right of the steering wheel and that, unlike normal paddles, is fixed, much longer (following the contour of the wheel), and actuates on both directions (pull for gear up, and push for gear down). This kind of gear shift is very common in rally driving nowadays. It could have an adjustable desk clamp, so that you can use it with any model of steering wheel, simply by attaching it to your desk or cockpit's steering wheel tray and then adjust if exactly where you want in height and depth.