Two additional points (edit. reading more carefully, these were touched already, but just to state again):
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Bidirectional communication for smooth update of the fader positions is not always trivial unless you’re talking about software that specifically has support built in or allows for extensive programming. Eg. many of the DAWs have something like Mackie Control protocol implemented, and Norns with its custom scripts can naturally do whatever the hardware allows. It just might not be a very “generic” solution, which I suppose isn’t a problem.
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Motorized parts may pose other additional troubles for firmware developer - eg. if an user grabs at a moving fader and tries to move it to the other direction the firmware would probably need to recognize that and release the fader instead of trying to wrestle with the user and cause damage to the fader / motor.
FWIW, The Uli Company -tm- does have several inexpensive controller models with programmable mapping and motorized faders, eg. BCF2000 and the X-Touch series. So if one wanted to experiment with a motorized fader bank with eg. Norns, and had no qualms about buying B* products, there’s already hardware one can buy and try to adapt for the purpose.