I can see all sorts of problems here.
1/ it would only take a few drivers to start using this and it would jam the roads up for everyone else. bit like making ever 20th car tow a caravan.
2/ If insurance start loading cars without boxes you will have no insurance if you take it off.
3/ Performance cars as such will die with electric. already a lot of tesla cars will leave any RS for dead....
The plus side is this is all about a few safety campaigners with a chip on their shoulders about cars. They blindly try and save the world by cutting speeding while ignoring drink driving, using mobiles, tail gating and everything else that causes accidents. what they dont get is if your car controls the distance between cars, auto brakes, keeps you in lane and blows your nose for you then we dont actually need speed limits at all as you have removed the human error factor.
Once again in this strange world we live in a few people, a small minority will over rule the majority, 500 campaigners will beat 20m motorists
just like 500 MP's will beat 17.5m voters.
6 lonely people on a council will get the speed limit reduced on your local A road and 20m drivers will not get a look in.
The real worry will be the government collects 10% of all tax in the form of fuel duty, nearly 30 billion a year and if cars are electric they will have to collect it from the motorist some other way which is why black box trackers built in from new will be inevitable so they can charge you by the mile and will include road tax..
Consider this as well. Its very unlikely cars will be owned by individuals. Leasing will be the norm because used values of electric cars will be nil as charge packs will be a major issue after 5 years.
Last one to jump off Beachy head, please turn off the lights