Whatever mode and over whatever route are not the deciding factors where 769s will run. They would be overkill using 4 carriages for most of the day on Maesteg to Cheltenhams. Keeping them on the Rhymney to Penarth means that only a limited number of traincrew would have to train on them rather than the need for widespread training.
That makes sense for now. My point was that,
were they to be retained (which as it stands they are not), they couldn't run Rhymney to Penarth anymore due to the non-continuous wires and the fact 769s only self-power mode is diesel. But,
were they to be retained, they could theoretically run Maesteg to Cheltenham and the diesel+electric bi-mode capability of the 769s would be useful on that route regards of any other pros and cons to deploying them thus.
At least it looks like TfW havent made the same mistake that Northern did with the 331s, by acquiring a train that would be creating diesel pollution until it is scrapped in 30+ years. The 231s will, I presume be convertable to Bimode, BEMU or even straight EMUs without replacing mechanical parts of the transmission.
TfW have made an even bigger mistake than Northern. Northern ordered 58 class 195 DMUs which (given a 30 year life) will create diesel pollution until around 2050. TfW ordered 77 class 197s (ie. 19 more DMUs than Northern) which if not cancelled sharpish, given the same 30 year life, will be burning diesel until 2052.
See the thread CAF Civity DMU for TfW....
Not enough tears. The introduction of all 77 class 197s, should it happen, would be a tragic embarasment for the rail system in Wales.
Here's the topic topydre mentions.