I actually think it is plausible that governments and/or Facebook do this, and it becomes widely enough adopted.
A community-level risk score would already be helpful (“based on estimates in your locality, the risk of contracting the virus when taking a bus is X now...) for individuals.
Are there attempts to build an app that tracks everyone by GPS, and notifies all possible contacts (and people having been in the same supermarket etc.) when someone develops a cough?
It seems to me that, with a majority of people using such an app, the R0 could easily be pushed below 1 without too many restrictions. I think this could even work when using the app is on a voluntary basis—I guess that people making wrong statements in such an app and getting someone sick amounts to negligent assault in many countries.
I don’t believe the claims that 60% of people getting infected—or even a month-long quarantine for everyone—is unavoidable with such a technology, and would like to hear differing opinions/see data suggesting the opposite.