HIlariously bad idea! I'd think maybe a bit less jostling on the desk, and maybe put pneumatics on the chair as well. I'd also skip the duct tape and bolt the monitor to the desk, and frankly I'm surprised the monitor stand didn't just snap off! Some sort of monitor arm that helps to absorb the shock of the "horse" would be a good idea.
This is the most ghetto motion sim rig I've ever seen and I like it! (I'm one of those sim racing people) The actuators hitting his garage floor sounds like horse hooves, clopping along.