Absolutely can be done.
But, you wouldn't use it to simulate the backcheck.
My interest in this is primarily to envision a keyboard with multiple touch settings available, and more importantly an interface that enables the user to adjust individual touch parameters to isolate tactile extremes. Being able to jack up the damper weight with, say, 200 grams or changing the jack tension, slope or position in the key dip would be an indispensable tool for passage work practicing.
That - and, while not related to electromagnets, a synthesized VST consisting of a trimbre that evolves dramatically and canonically as a function of the progression in velocity, especially across the quiter velocity range, emphasizing the near imperceptible dynamic differences - would be very useful means to aid in objectifying the work done on phrasing and harmonic animation.
Modern Player pianos already use electromagnets to play the keys.
Thats news to me. I will have to look into that.
Yes, for sure "low demand" is part of why it's not on the market.
The fanatics enthusiasts, here, might be really wow'ed by a digital piano that could match an upright action, or a grand action, or an organ, by pushing a button. And some would be be willing to pay for it.
For the vast majority of DP buyers, it wouldn't be high on their list of "wanted features".
Then again, a real grand action is not cheap either. Would be interesting to have a rough estimate on the cost and a rough idea of what it would require to build. Perhabs the application and development of similar technology in other fields could bring down the price in the future?