I like the idea but I'm skeptical. Not sure how it'll work, but any GPS app I use regularly messes up the speed limit, be it due to construction (or sudden lack of) or just 2 roads being too close and me being on the other one.
And when reading signs with cameras, there are some speed limit signs with additional information underneath specifying a time or anything really.
And then finally all the times when the signs are barely readable or even just wrong. I legit can't count how many times I've seen a speed limit sign 10 meters before a series of junctions with an end of speed limit at the end of this ordeal, like that's not how this works, what the hell?
Edit:
Just remembered the extremely silly cases of speedlimits. Once saw a 10km/h limit in a parking house when going up hill to the seconds floor. Just for shits and giggles I tried it, I almost went backwards trying to fight gravity, so glad no-one was there at the time, also just took forever.