This interesting 28 MPH e-bike conversion kit uses a totally new design
Amazon.com : RiToEasysports Bike Disc Brake Kit,Aluminum Alloy Bicycle Disc Brake Conversion Set Brake Lever for Road Bicycle Mountain Bicycle(Black) Bicycles and Spare Parts : Sports & Outdoors
Disc brake conversion kit - Nihola
Skarper's revolutionary ebike conversion kit uses a disc-brake rotor to drive your bike - BikeRadar
Retrofit - Disc Brake Conversion — TI CYCLES FABRICATION