The design in the OP is still more appealing (if less practical) to me because its movements and how it plays are still fairly close to how a human would play (Precisely because of the sliding). Sort of like how we generally find it less interesting when a specialized robot can perform some specific task rather than say a humanoid robot, even if it is worse at said task.

I suspect that the software could address that. We can "humanize" MIDI files, after all. (Not to mention that we can prepare them by capturing performances.)

I'd like to hear a simulated slide by a ripple sent to the fixed-position actuators; would it be convincing?

This sounds even more like a machine than the Kuzma though.