Interesting concept. I feel better about contract tracing after reading it. It leaves me with some worries though. (leaving aside the big brother worries for the moment)
The big question for me is that bluetooth range is 10 meters or so. 10 meters is is much greater than the range necessary for safe social distancing (2 meters). I live on a corner. I am typing this from my office which is less than 10 meters from a sidewalk intersection where roughly 30 people walk past per hour. A good portion of them will be within BT range long enough to send a gibberish message (or get one from me) . So a ??% chance of getting a gipperish blast from each of them which works out to ?? per hour and ??? per day ( numbers depend on how often the gibberish happens) . Within 14 days, I have ??? gibberish messages and only 6 of them need to be covid-19 for me to get the dread message to isolate. An yet, in reality, I am not at risk of infection from anyone who shared those messages.
It would not take long for me to get the dread message. After that, my phone becomes a beacon of false alarms for some % of those who walk past. It only takes a few of them to walk past often enough for their phones to also become beacons of false alarm. Soon, any trip around the block becomes a sure way to get the dread message. An yet none of us may actually be infected.
This false alarm potential due to bluetooth range when applied to the real world (vs me in my office) seems likely to cause a high number of false alarms. Just sitting at a stop light or riding public transit, or practicing what is currently considered safe distancing provides have plenty of plenty to get some number of gibberish blasts. If this happens often enough, it amounts to the same thing as asking everyone to just isolate and naught it accomplished. People in urban settings where isolation would be most beneficial will have the most false positives from the range issue. Unless they can fix this issue, this is doomed to fail.
Also, it may give a false sense of security. You become contagious through some means that is not caught by this method (someone not playing along or by not washing your hands after touching something with the virus on it). Thus, you do not get a message telling you to isolate. You fail to social distance thinking everything is fine when you have actually become a vector and are emboldened by the lack of a message.
It also counts on people becoming symptomatic and on symptomatic people reporting to the system. Some with mild symptoms (i.e. not seeking help) may avoid reporting as they want to avoid the scarlet letter of plague carrier being attached to them. (the same sort of people who hide zombie bites).