However, 3 wheelers quickly reach their limitations in turns, since you can't lean to balance. So making a C5 go much faster than its original top speed could be risky.
I don't think the speed would be an enormous problem; the legal (powered) speed limit for e-bikes in the UK is essentially the same as when the C5 was new, at 25km/h. So as long as you stick with a stock EU/UK standard controller you should be fine.
And you'd get a fantastic amount more grunt uphill and a longer range with a modern battery and motor.
Could the car lean if it had electric suspension? Is this a fundamental limitation of a 3 wheeler with 2 in the back or is it just difficult to achieve?
“On BBC's Top Gear programme in 2002, Jeremy Clarkson said, "I have to say, absolute hand on heart, I've never had so much fun in a car, really and truthfully, and I don't think I'd ever tire of it."”