Hi
Welcome to the forum!
Nice work with the 3d model.
There have been variants of this suggested before and I considered it myself for a while. If you think about it though it doesn’t actually work to dissociate the up-down movement of the axle from the rotation of the cranks, so the wheel moving up and down will cause the pedals to rotate. If you consider your feet and legs on the pedals resisting this and you sitting on the seat, it is still essentially rigid, probably with a lot more stress on your knees. Think of hitting a bump, this will cause the suspension to move up, causing kickback in the cranks – if your hip position is essentially fixed because you are sitting on the seat, one leg needs to get shorter and the other longer so you will not be able to smoothly pedal the unicycle. You could counter this by not sitting in the seat and keeping your feet on the pedals but you’ve then essentially removed the suspension from the system.
See the post I’ve linked below for another explanation and various other discussion.