Something like this might be useful, if instead it was just a display of the current speed limit. Drivers would/should be able to tell when it's pulling the limit from the wrong road and not do 65 mph on the country road next to the highway, or slow to 25 on the highway next to the country road. Incidentally, both of my relatively recent cars with built in GPS do this, although the data is fairly low quality.
At the end of the day, there are times where you need to exceed the speed limit to drive safely; and there are plenty of times where exceeding the speed limit is not unsafe; anything built on the principle of strict adherence to arbitrary limits is going to result in bogus outcomes. This is much worse than the generic speed limiters around 120 mph; that's fast enough that it's pretty unlikely you'll have a case where you needed to go faster for safety reasons.
At the end of the day, there are times where you need to exceed the speed limit to drive safely; and there are plenty of times where exceeding the speed limit is not unsafe; anything built on the principle of strict adherence to arbitrary limits is going to result in bogus outcomes. This is much worse than the generic speed limiters around 120 mph; that's fast enough that it's pretty unlikely you'll have a case where you needed to go faster for safety reasons.