Interesting idea. I think most people will hate it and there are many technological reasons for it to be problematic.

Can it be abused too? Say I have an old car without that limit, harass or attack someone then speed up by only going 15 over the limit? What about emergencies? What about motorbikes in that law?

A ton of unintended consequences to consider.

However, I don’t think any car needs to be able to go over certain speeds, and that could be a place to start. Would the limit be 90, 100mph?

Maybe get a way to unlock on a race track, but beyond that, some advertised top speeds are absurd.