Turbos will remain in Thames area and fill in for 387s working HEX
Always the plan until Crossrail came in - 769s were
never intended to directly replace 387s.
Instead of 769s releasing Turbos releasing 387s, we now have Mini-HSTs releasing Turbos from the
West releasing 387s - 166202 has already recently transferred back East to support the 387 mods programme.
ASLEF and GWR are working through some issues with the 319s, which will also be applicable to 769s - this has put a pause on 769 procurement for GWR until those modifications to the 319s are delivered and certified - although that was last I heard to be partly mitigated by jumping onboard with TfW for driver training, and using the 319s for majority of driver training - compressing the lead time from units being accepted and EIS.
The issues ASLEF have raised are common to both fleets; so not really a 769 programme problem.
Long term there aren’t enough vehicles in the GWR fleet, 769s will have to be made to “work”, and significant pressure is being placed by GW on Porterbrook and Wabtec/Faively to get on with it.
Some of the planned enhancements to Thames Valley services (in particular enhanced peak Basingstoke service and 3tph North Downs) have been partly or wholly descoped from December TT; with rolling stock availability a main concern in that decision making process.
Late 2019 is the date I’ve heard for first unit delivery; with EIS on 8 diagrams from Spring 2020 - a change from July 2019/Dec 2019 respectively.
EDIT:- and no use of DC electric equipment for infrastructure reasons. Use primarily in Diesel mode; with AC available on Western route infrastructure (although minimal work on AC routes)