Thanks @caelmore and @oot I will search in this direction. These ribbon sensors from Adafruit are really interesting. I could also try to open the DSI pro 2 and see if it uses something similar or if it uses a series of small capacitative sensors but the sliders on this synth are also pressure sensitive, so it might be something a bit more complex, but I like the idea of a ribbon controller. Now that I think of it, the Tetrapad uses a similar tech as DSI. But for the sake of simplicity, the Adafruit sensors could be just fine for a small module I guess.
More generally, I wish I knew what kind of parts/sensors are used in MPE devices like Roli, Linnstrument, KMI, most probably very custom parts etc but that’s another story haha 