Some interesting points about the flaws and problems with contact tracing apps. I can relate.
I live in a second floor flat and can see many of the flaws mentioned happening here: When pairing Bluetooth I regularly see stuff I don't know who owns it, could easily be one of the flats either side of me or the flat below me (I'm the top floor, so there can't be anything from above). Should they decide to just use location (nothing is impossible with the imbeciles in our government...) I would be in exactly the same place as the guy living below me and the folks on the ground floor. I think over the last couple of months I've met the guy living below me twice in the staircase, the people from the ground floor I think I've only met once.
When I go out for my daily exercise walk most of the people I meet are regulars with the few odd ones out thrown in. So I won't know which one of them triggered the alarm, so I can't think about the meetings I've had. Most are very good in keeping their distances (in particular the regulars), although some are closer than I would like. A few days ago I had a 5 minute chat with one of the regulars. He is one of the best in keeping distance, he almost jumps into the canal while I'm hugging the fence on the other side of the towpath. While we were chatting (after we had passed each other) I estimate we were more like 4 metres apart, if not even 5 metres. No distance for Bluetooth. But I suspect the app would trigger an alert.
Considering all the crap and fake Coronavirus news I've seen being shared in particular on Facebook I wouldn't be surprised if the Russians and other actors would jump at the opportunity, Not to mention all the pranksters. I predict they will get very creative, very imaginative. They will come up with all kind of schemes to create alerts and panic, schemes not even the security professionals have thought of yet.
Apple already has this kind of technology with it's Find My device feature. If you lose your phone and Find My is turned on, it communicates with any other iPhone and/or iPad in the area using a combination of WiFi and BlueTooth, and those devices help in locating the lost phone to within a fairly small area. I've no idea how it copes with height. Perhaps it also includes data from the built-in altimeter. My guess is that Google will build similar tech into their app, and eventually into the OS.
It depends on your activity is the most recent statement. You'll need more than 2 Meters (or whatever feet) from joggers for example. Or mountain bikers. And check the wind direction, as I said, when passing them ;-0