I remain to be convinced as to the 769s suitability as Turbo replacements - particularly on the steep gradients of the North Downs. They also won’t be able to replace the Cotswold unit, Marlow and Greenford branches. So Reading will *still* need Turbos.
Crossrail will ultimately release 22-24 387s; once you account for the Hayes, Readings, the Maidenhead peak extras, changes to the Didcot locals and so on. Ample to account for future capacity increases, Newburys, possibly even the Henley and Windsor branches. Now while it wouldn’t enable a 2nd Turbo cascade; a temporary, short-term small fleet of AC EMUs to release the 12 387s for HEX conversion would be all that’s required. Something readily available, and similar to GW’s existing fleet would be ideal. Much easier to train maintenance staff and drivers on something similar to what you already have, than a wholly new type. Now if only there was a fleet of AC Networkers in storage somewhere....