coming back to your idea

Despite that the objective sounds a bit too massive to attain, at the moment it does seem realistic to me, from the tech point of view.

Question about privacy is more from the legal side - this is an intrusion into the personal life, without a consent. Even if the system is distributed, people who maintain it are at risk. Surely it is likely that govts might have some similar systems, but they don't go public with them.