Bluetooth uses frequency hopping, which is unsuitable for measuring TOF. This group tried it: https://hal.inria.fr/hal-01995171/document and even with a lot of cleverness they were seeing 100 foot RMS errors from Bluetooth. Not enough to prevent stealing someone's car parked in their driveway while their phone is in the house.
They’re using unmodified hardware and minimally modified software. It would be interesting to see how much precision could be achieved with hardware modifications.
Instead of Bluetooth (which Apple could totally fudge on their own devices if they wanted to), the TOF for the Apple Watch<>Mac auto-unlock uses Wi-Fi 802.11v. It seems really quick too (presumably the Mac is establishing a short-lived AP), would work fine for unlocking a car.
