Just got off the phone with Gary & Scott at Horstman. The axle clutch is still very much a go. It may not be available to the sprint sit up road race crowd due to stall speed rules but it will be available in for the Laydown crowd for 1 1/4″ axles.
Clutches should be available mid January 2017. Target price is in the $900 range.
Gary told me the staff at Horstman would be more than happy to discuss the project with anyone. Just give them a call