Is it possible to buy a traditional pedal rickshaw and stick an electric bike conversion kit on it? The rickshaw I've seen is the type when the rider is at the rear and so has two wheels at the front and one at the rear.
Tadpole-style trikes with one wheel in back are quite easy to electrify.
You can either use a rear hub motor or a bottom bracket motor. Given the high startup torque requirements with rickshaws and thus the desirability of low gearing and a range of gears, I’d recommend a bottom bracket motor such as a Bafang BB - the only concern is if there’s enough clearance to mount the bottom bracket motor around that frame. This allows you to have a pretty good range of gears using a rear derailleur or internal geared hub such as a Rohloff on back.
You can reprogram a BB motor controller so that max assist is limited to 250 watts or max assist speed is limited to 30 kph or whatever your local laws are. Proving that your assist is limited in such a fashion to a constable that is trying to write you a ticket is another matter.
Hub motors that have two or more gears are available but their long term reliability is still unknown — and even with gears, hub motors unfortunately don’t have great starting torque.