Here is my explanation of the idea.
A rack and pinion mechanism is what I use in the video, but a lever mechanism could be used as well. The main issue I have is being able to fit enough gearing to convert the small amount of vertical distance to the large amount of horizontal distance required.
The gearing has to be set up correctly so that there isn't too much input torque needed to overcome the gearing. For example, I weigh 165 pounds and if you're using a 1 inch pinion then I will get a torque of around 9 Nm. The input torque required for the gearing ratio cannot be higher than that. With those restraints I believe that using a large wheel on the output is best, since it reduces the gearing needed.
I am currently working on my other VR shoe project but want to eventually try to make a working version of this concept. If I can, this VR shoe could be very cheap to produce.