The newest version of Bluetooth adds Direction Finding, which enables a Bluetooth LE device to determine the location of another nearby Bluetooth LE device with accuracy as good as 1cm. Direction Finding requires that one of the two Bluetooth LE devices have multiple Bluetooth antennas.
Two new Bluetooth profiles enable the capability: Asset Tracking Profile (ATP) and Indoor Positioning Profile (IPP). In phones, ATP requires multiple Bluetooth LE antennas in the phone, and enables the phone to determine the direction and distance of nearby Bluetooth LE tags. Such tags might be attached to valuable or easily-lost personal property, or used in settings such as museums, to enable apps to show info on items as you point your phone at them. (Previously, phones could only determine the relative proximity of Bluetooth LE tags, not their direction or precise location.)
Phones that support the new ATP profile are not expected until 2020. The IPP profile enables a form of “indoor GPS” with centimeter-level accuracy. It does not require multiple antennas in the phone, but does require new location beacons installed in indoor locations — such as malls and airports — that contain multiple antennas and explicitly support IPP. Some existing phones may be upgradeable to support IPP.
Bluetooth 5.1 includes a several other minor performance improvements, but Direction Finding is the primary new feature.
