I’m into this concept! Here’s a quick thought on how I’d approach it.
Using the spur gear you linked, but actuate it with a worm drive on a high torque servo. Probably enough torque to be able to crank down on the nut. This approach also keeps the overall package size fairly compact and could be mounted with a 3d printed jig. Then using @RipTideSports KranK would be perfect because of their pressure-hardening qualities. You could could a large degree of variability with 1.5-2 rotations. Then like you said before, dynamically adjust the nut position (bushing hardness) based on speed with a little closed loop mechatronic system.
Hope you make a go of it!
EDIT- Thinking about it more, the hardest part may be a sufficiently responsive system. Our boards accelerate pretty damn fast, would have to do some prelim testing to see if this system could even keep up. That said, it ~feels~ viable.
EDIT EDIT - lol yep, variation discussed in the other topic on truck angles.