Something I've known about for perhaps a week are these FSLPs:

These are the only ones I can find, which are allegedly 100 x 10mm, though the black film certainly looks a lot wider than 10mm.

Today, I've found out that there is a thin-film style of potentiometer, and it seems only one manufacturer makes it commercially:

I also assume that, unlike FSRs and the aforementioned FSLP, it's not cuttable.

Below, I found some videos of people layering these pots ontop of an FSR:

While I think it would be nice to be able to just touch anywhere on the belt and Tetrinsic can sense exactly where, I see it as an added luxury considering that the price would be a considerable percentage of the BOM and the position in day-to-day use is already acquired via the magnetic encoder on a motor.