California tried to do this, the bill got watered down in committee [1]. It's probably true that purely GPS-based speed-limiting is not good enough. Imagine being on a 75mph highway with a 25mph service road right next to it and the GPS not knowing the difference.

Still, interesting idea that could have legs when the technology got better.

[1]: https://www.npr.org/2024/09/05/nx-s1-5099205/california-tech...