$6 later, the magnet idea looked like it would get a $65 million investment on Sand Hill Rd, but was a failure, at least with the readily available magnets.  The keyboard effortlessly pressed them right together,  even with 2 magnet assemblies.  Previous experiments showed the repulsion distance doesn't change significantly until you get into life threatening sizes.  Undamped systems have bigger problems.

Another $5 & the mighty C-812 spring managed just a low enough stiffness to do the job with 1 spring.  Unfortunately, power chords at the right tempo made explosive oscillations.  Damping systems can quickly become absurdly complex.