of course, it depends what you want it for.
a lorry brake would be a good start and simple to do. Mount is ont a frame connected to pto and then something to gradually apply the caliper.
just be aware of how much energy your trying to work with though.
a tipper wagon has a brake on each wheel (8 off) to hold back 32 tonnes. I accpet the difference in speed is great (kintetic energy is the square of the speed, but as a retarder your maintaining a steady speed, so the rest is true), but your thinking one brake disc to hold back a similar weight.
However, i think it would be very worthwhile to do. not sure how you would actuate the caliper, as hydraulic control on a spool would not be sensitive enough?? maybe electric actuation?
Just bring back fergy pressure control, was magic for brakes back in the day and be perfick for this application