> It is amusing that the BLE tracing toolkits were sold as a way of not having to expose your location data to Google and Apple, the exact entities who already have fine grained location data on most people.

I think they were sold as a way of not having to expose your location data to government authorities. Also, Apple makes a fair amount of noise about not collecting fine-grained location data and other PII on their servers; as far as I know, at least, they simply don't do the kind of server-side logging that would let them do the kind of historical reconstruction you're describing in your first paragraph. I'm not entirely sure Google does, either, for that matter, even though they keep a lot more server-side.

(Foursquare, of all companies, could probably do it. But only for a too-small subset of people.)