"Cutting all Power" should mean cutting additional gas that accelerate...or I mean it just work like cruise control that instead of supplying more gas when it goes under speed, it stop supplying more gas when it goes over the speed.
Thats how it works, power to engine is reduced to limit your speed.
But requiring GPS?
It needs GPS to match the speed limit to roads. HGVs, some company vans, buses, etc in the UK have a limit set like you said. For HGVs this is 56mph, for some vans its 60 or 70. In the case of the HGV this is to make sure it is not driven beyond its safe limit. With the others it stops the vehicle going over the national speed limit.
However, the GPS based system will ensure that the drivers can not (when it is enabled) exceed the speed limit on any road. The tested version has a "warning only" mode, but presumably if this gets used nationwide by large companys they will enforce it, as they do now with HGV limits.
Why do we need to pull GPS into the picture? I have absolutely no idea.
Imagine a taxi driver (im probably being a bit prejudiced, but in my experience they frequently speed on 30mph city roads) - he would have to follow the limits regardless of how many customers he wants to have in the shift. This of course cant ensure good driving but its a step closer.
I want a camera to record where I go and what I do and act as a backup for my cranial memory. I want it to recognize faces to keep track of my history that person.
Facebook handles that for you.
I want an internet connection everywhere so that I can call up an alternative recipe on the fly when I realize at the last minute that I'm missing an ingredient.
Recipe iphone app?
I want to use the sum analyses of my automotive commutes to recommend ways I can change my driving behaviour to extend the life of my car and use less fuel.
Why does that have to be HMD or wearable? Just use a GPS (or your phone) to track your journeys and suggest new routes.
So.. You can pretty much do what you want already. You just have to give up your rights to google, facebook and apple, and have to look down at a screen now and again.
I think we have to accept that yet again the future will not be exactly as predicted (or as cool), but will accomplish similar goals and be cool in different ways in the end.
You have a tendency to feel you are superior to most computers.