Sure, but now you can track someone from their car through public transport, shops and god knows wherever else someone placed a sniffer.
And no, randomization doesn't help, because in the end the Find My beacons have to resolve down to some common identifier otherwise the "an unknown device has been following you for 2 hours" warning would not work.
Not really, this is actually pretty easy. If such a device beacons and a trusted device is within range the trusted device can respond to the beacon and let it know it's nearby, then it just counts up if not. X number of beacons with no response, set the "not near my trusted device" flag. Some other device sees X number of beacons with that flag set while moving around, send alert to the user.
So yeah, if they subponea/coerce Apple (or Apple signs up willingly) they could track people individually.
But at that point we’re no longer talking about large scale tracking by an untrusted third party. Apple and my phone company have always been able to track me without getting license plate scanners involved.