I think that would be tricky in practice. For most ebikes the m factor is going to be dominated by the rider's weight, not any property of the bike itself.

Plus if you limited bikes to something reasonable like 20mph you'd have to start limiting cars to ~5mph.

I'm pretty sure we already limit cars to zero miles per hour in parks and on sidewalks. :p

That said, yes, there are some dangerous trends in car (un)safety to pedestrians.