Update, late April 2021.
Hammersmith Bridge Taskforce meeting, 29 April 2021 - GOV.UK (www.gov.uk)
(i refuse to keep opening new threads on the topic!)
Just received that latest PLA .PDF.New bridge signals installed, similar to those bridges by the Thames Tideway Tunnel Sites:
Upper Notice - U3 of 2021 - Barn Elms Reach - Hammersmith Bridge - Closed to Navigation, Exclusion Zone & Controlled Transits
Still need to book 72 hrs in advance.