FWIW, Shimano's roller brakes have similar specs.
Forks need to be stiff enough since they have a torque arm similar to a coaster brake hub. I don't think they need special bosses like disc brakes, however.
I think Shimano makes a roller brake specifically intended for wheels 24" and smaller. I suspect they'd have to be special ordered.
The couple data sheets I've seen Shimano recommends a weight limit of 100kg. Such weight limits would pretty much rule them out for heavy load bikes such as tandems or cargo bikes.
The use of a torque arm pretty much means that they could only be mounted in a specific orientation.