The Proxbook report on "Proximity marketing in airports and transportation" states the following concerning Munich airport:

The installed hardware includes 120 “bluloc Big Bays”. These “power beacons” [..] make the transmission of signals possible for distances up to 100 m. [..] The beacons also enable to“sniff” WLAN and Bluetooth-data within the reception radius. The data that can be collected includes timestamps for entering and leaving a defined zone. As a result, it is possible to measure visitor streams without the visitors using an app

This is of course just one example of existing deployments of vast arrays of Bluetooth sensors alongside other means of collection of more direct identifiers (security cameras, tickets, etc). Another example could be the deployment of "smart" advertising panels in the subway, or more exotic deployment of roving Bluetooth sensors in taxicabs in a city full of security cameras. There are very many possibilities according this New York Times report and no good reason to expect the situation is very different in Europe (see for instance the company Fluxloop and its high profile European clients, such as advertising panels JCDecaux).

These are obviously relevant as security actors, but they are also relevant to the data protection assessment because there are vast and already existing deployments of Bluetooth passive antennas.