TfL planning document reveals the transport body’s hopes that all three plans — mobile coverage underground, the fibre network, and 5G support — would help fund the transport system: “Our expectation is that the commercial partner will cover the capital and operating costs of the telecoms operation and would provide a revenue share for us.”
It added that mobile operators said no customer data would be “directly available” from the proposed system, though TfL noted that they “offer aggregated, anonymised data services.”
Commercial partners are expected to be signed up by this summer, with an incremental rollout starting by 2019. TfL said all work would be carried out within engineering hours so there would be no disruption to train services.
I think the idea is proper mobile (3G I assume and definitely 4G) coverage, not WiFi. There *is* a difference.