I would think that an emergency stop mechanism would be a whole different magnitude than a scheduled, everyday, stop.
For a finger saver an emergency stop mechanism would have to stop the blade in a few teeth passings. For everyday usage a couple dozen blade rotations would be OK too. These two situations would require different tactics.
A dynamic electronic brake could vary the intensity for the two different scenarios and we could add the caliper to the emerg stop. A caliper probably wouldn't last long in everyday usage and would need to be adjusted and/or replaced frequently.
I would also think an assembly with wheels applying just a little pressure to the sides of the blade would make a decent passive system. It would be just enough pressure to slow down the blade in a second or two and not enough pressure for the motor to even register the resistance.
Think about how little pressure it takes with a scrap piece of wood to stop a coasting blade.