Interesting article. The IBM PC sort of dates it though.
It would be a big consumer of air since the valves are constantly cycling. Pneumatic brakes are neither legal or illegal. You just need to use an legal pneumatic cylinder to actuate it. It can be an integral part of the brake as long as R77 J is met. The equivalent rule in past years was a lot tighter for passed for a pneumatic actuator.
A closed center valve works well for positioning assuming the dynamic forces aren't too high. The trouble is R89 requires the system to fully vent through one vent valve. R82 has an allowed working pressure of 60 PSI. A closed ended cylinder might exceed that. Since check valves are legal this year, you can comply with the rule by clever use of check valves to vent the closed ends of the cylinder back to the working pressure line. R90 will not be violated since you will be plumbing the outlet of the control valve to the inlet check valve.