Magnetic repulsion?

In order to float a heavy plinth, the magnets must be able to generate a very
strong magnetic field. Cart is very sensitive to magnetic field. Unless your cart is
well shielded, given the close proximity to strong magnetic field, the result
could be disastrous.

I see a new audiophile gizmo! Turntable with superconducting magnets. But the liquid Helium tanks would have low WAF.

There are several commercially available turntables that sport a magnetic suspension of the platter. See especially the Verdier La Platine. It's not a new idea, and it's not a perfect solution to the problem of a vertical bearing, but it can be made to work well, as in the La Platine.

I've played with pair of 3" ring magnets: it easily supports my 32 kg 4" thick platter placed below it. But the magnet field went up to 20 gauss measured at the record plane - to much! Three layers of mu-metal sheets did not help much. There is another inherent drawback: magnet repulsion is essentially unstable; every minor deviation from perfectly concentric magnet fields (unevitable) produces considerable side force applied on journal bearing, increasing bearing noise. So I finally abandoned this idea.

also since the magnetic field is slightly changing a voltage source is created by Faraday's Law. not certain of the magnitude but it could interfere with the cartridge voltage, remember that a MC has tiny fragile voltages. i would think that the magnetic interference with the cartridge magnets would be much more significant tho. but then again MC carts would be very susceptible to either magnetic or voltage changes. all it's really doing is creating a spring mass system anyways. the platter would just oscillate about its equilibrium point.