"We don't want something that only allows people to be notified on their devices without anyone knowing who they are. We want to know exactly who the contacts a

"We don't want something that only allows people to be notified on their devices without anyone knowing who they are. We want to know exactly who the contacts are" Why??? And even if you want the authorities to get specific names and contacts (which I don't understand the usage of it), a system giving those name while not revealing with whom s.he had been in contact with would be good. More you have privacy, easier it gets to convince people to opt-in. Monero or Pirates blockchains allows you to do some transaction while obscuring sender, recipient and amount of the transaction... Seems an inspiration to get more privacy for tracing app