I still use Pis in my 3d printers. Laptop would be too big, and a ESP could not run the software. "China clone" might work, but the nice part of the pi is the images available. It just works™
I'm also currently building a small device with 5" touchscreen that can control a midi fx padle of mine. It's just so easy to find images, code and documentation on how to use the GPIO pins.
Might be niche, but that is just what the Pi excels at. It's a board for tinkers and it works.
Yeah sure, for niche use cases it's the best and only choice, but that's why it now commands niche prices ;)
You can run Klipper on any Linux SBC with a USB port, RPi works but so does an old router that supports OpenWRT, a cheap Android TV box that could be flashed to run Linux, or any of the OrangePi/Banana Pi/Alliwinner H3 boards. You don't really need hardware UART because most of the printer boards you'd be using have either native USB or USB to UART converters. For that pedal, would an old Android tablet that supports USB OTG work? Because that's got to be much cheaper, and with much better SDK.