Full-on driver-only operation means just that - no other member of staff on board the trains.
What the then FGW said in 2015 was that it wanted the drivers to have full control of opening and closing the doors - it was made quite clear at the time by GWR that there would continue to be a train manager on board IET services other than the Oxford route and, as I said above, that there would be more train manager duties on the Oxford/Cotswold route because a number of existing DOO Turbo services would be replaced by IETs.
The full letter from FGW to staff is in a thread here somewhere. It said something along the lines that only in exceptional circumstances would a train operate without a train manager - though that if that was the case in practice, it may well have helped ease cancellation problems on occasion in recent months when an IET-trained train manager was not available.
Frankly, after what Southern's 'integrity' has done for rail services generally in that area and passenger numbers in particular, then a pragmatic decision to avoid a repeat of that in the GW area seems an eminently sensible approach to take.
That the RMT apparently still won't leave things alone over what will be a limited number of DOO services on a single route where DOO operation has been a fact of life for 25 years - and will be at a reduced level in future anyway - is just silly, frankly.
It doesn't sounds like an easy puzzle to solve. Reading and to a lesser extent Didcot are crying out for extra capacity. The morning peak trains are already so full they often can't be boarded and there aren't obvious paths for any more as the main line track capacity is saturated once the 4x HeX are brought into play. Run 5cars off-peak and they need to be doubled up somehow in both peaks, as for splitting as constrained locations like Swindon or Oxford - sounds like a real tangle. Since First Class was reduced, the HST is more like 460-550 standard seats so far in excess of a 5 car IET. The prudent approach might have been a mixed fleet of say 6-7 & 10 car IETs if the peak / off peak duties could be separated on the grounds that 6-7 to Cheltenham off peak is no more overkill than today.
The reason behind the five/nine split is simple enough and was discussed previously in the Class 800 thread - near enough having the same passenger capacity on a 2x5 formation and a nine-car, and actually fitting the trains into the platforms at Paddington - 2x5 just about fits, 2x6 wouldn't.
There is plenty of experience of using five-car trains outside the peaks on the Cheltenham route, in the shape of 180s (which have 40 fewer seats per train) - and at the current two-hourly frequency - without overcrowding problems, so I don't envisage any in the future with a train every hour, plus 2x5 or nine-coach trains in the direction of the main peak flows morning and afternoon.
