[pasbesoin]

Whether alone (with user movement and precise clocking) or in a coordinated group effort, devices might begin to triangulate tower location and check this against historical and geographic data.

It would be a bit ironic, if/when triangulation begins to "work" "in the other direction".

[icebraining]

It already is: Mozilla has been building apps¹ that allow users to contribute to a shared database of the locations of cellphone towers and WiFi APs.

The idea is to allow GPS-less devices to find where they are, but it could certainly be used to identify new towers in places which had already been mapped.

EDIT: It seems there's also opencellid.org, which actually allows you to download the full database.

¹ https://location.services.mozilla.com/apps