This feature exists in my Jaguar XF. Similar to the cruise control, you can set a 'max speed' and the car will simply not accelerate past that speed. I don't think I've tried flooring it to see if it would let me exceed it in that case though.
Another feature is speed warnings, which "beep" at you when you exceed them. Currently they only seem to be singular, but it should be possible to integrate them with satnav and speed sign recognition. I expect these would be safer, especially if it linked up with a, "black box" to report excessive violations with a parent, insurance company, police etc.