A current mid-range brushless e-bike controller is <$150, 72v+ (up to 100v), 45a continuous, fairly waterproof, speed switches, programmable, regen-capable, and very modifiable. You can get an option cycle analyst to hook up the the controller. They are surprisingly good and surprisingly cheap for what you get.
controller
To beat that Castle would need to bring something new to the table (some are far-off)
-better programmability
-more power/reliability
-smaller size
-100% waterproof
-attractive display for handlebars
-data logging
-adjustable dc voltage (run 36v off 72v battery with flip of switch)
-gps
-temperature monitoring/cutoff (controller and motor)
-on-the-fly current/speed adjustment
-built in switch/pre-charge circuit
-voltage sources for lights, etc.
-vivid flames and raunchy green monsters