This is not pie in the sky science fiction to drool about. We could do it now. We could do it 5 years ago.
Of course, whether this would be popular with voters or car companies is another matter...
Machine vision, triple meh. Even with strictly standardized set of easily recognizable shapes, this is useful for post facto mapping ( https://blog.mapillary.com/tutorials/2017/08/21/mapping-traf... ), but nowhere near realtime without false negatives.
As for built in sat nav - I have three (3). Their notion of current max speed matches about 80% of the time...and that doesn't always match the actual max speed in meatspace.
This problem is a right-of-way issue, not a speed issue.
Slower speeds also give both pedestrians and drivers increased time to notice and avoid a collision.
Nobody ever thinks these kinds of statements through. It's just, oh we'll sign the regulation, and poof, everything instantly falls in compliance. No. No, the world just does not work that way.
however - we could force the issue of speed limits within city spaces for cars that are newer, like you said we certainly have the tech and any car with traffic aware cruise control should be able to have a limit forced upon it within city limits
We also have the technology to capture your license plate as you zoom down the road. Do we want to have tickets just mailed out for violating the limit? Perhaps make it random which roads are enforced so to make it feel as if all are enforced?
as for scooters
scooters stand a good chance of being out right banned in many cities. right now Atlanta has a curfew hours on them and considering that four deaths this year occurred on them as well as over two hundred responded to calls for injury I would not be unhappy if they were.