Perhaps if the tender GWR put out for thirty four-car EMUs does bring the thirty redundant 379s to the West, they can stick those on the hourly Cardiff services with their nice 2+1 first class and comfortable standard class seats, send the redundant 80x for the permanent crack repairs and onto Cardiff Plymouth Penzance to send the worn out and expensive Castle sets packing, and all while leaving the 387s as they are in the Thames Valley.
But until that happens, and sadly I don’t think it will, it’s all speculation; there is just no evidence to suggest such a move will happen, and there certainly aren’t enough 387s to provide a half-hourly London Didcot, hourly London Newbury, hourly Reading Newbury and hourly London Cardiff fast. Not unless GWR believe four carriage formations will suffice on all of those, and on London Didcot and London Cardiff, they most certainly will
not.
There are zero plans to transfer further services in Thames Valley to Elizabeth Line; who wouldn’t have the 345s to take on extra services anyway.
Apparently they don’t even have one single 345 free to knock off the knackered pair of 315 working one AM and PM diagram that could be so easily replaced, let alone taking over more GWR services
