I like the idea of having a mount up on the top of the chipper.
Since there is no throttle lock, there needs to be a way to hold the trigger and tension on the rope. If the capstan is mounted on top of the chipper, that means one person climbing onto the chipper to operate it.
A mechanism can replace a person and be easier to use.
There might be times where releasing the tension on the rope is not desirable as a means to stop the advance of the rope. For example if you want to 'fly' material, rather than skid it up a hill. You might be hoisting high up one trunk on a hillside, then transferring to another high set drift-line on another trunk above a landing.
Perhaps its just a hot-glue-gun project to put 'keepers' for a choking cord around the trigger, and a cleat for tying off the cord.