I’ve been following this with a certain “what the actual fuck” state of mind, since the main point still stands: Bluetooth in its current form does not allow such an app to work.
So, while everyone is discussing privacy and security and whatnot, RSSI simply will not work as advertised.
I’m still asking myself if I missed a very crucial part which would make it work.
I tried to contact some journalists who could possibly use their leverage to find out. I am at a dead end. I don’t know who to ask. My contacts either have no grasp of the technology and admit as much - or, if they have some, they tell me I should forget about it because it won’t work, causing massively false negatives and comparatively massively false positives.