Thinking about the obvious (if not critical, IMO) need for customized templates, I’m wondering if using static cling sheets would be an interesting solution. E.g. these:
Cutting holes in them would probably be important for things where you want your finger to slide (like sliders) on the bare surface, and there now appear to be inexpensive cutters that might easily do the job:
For small custom runs, there are services that print such things:
https://www.uprinting.com/window-cling.html https://www.buildasign.com/producttype/windowclings/Make-Your-Own-Window-Clings https://www.stickergiant.com/static-cling-decals
This solution would not have the benefit of having the magnetic detection mechanism that the “real” Sensel templates have, but the flexibility and quick production of templates would, I think, far outweigh that benefit.