Apparently abbey foregate is getting 2 more roads reinstated, as tfw and wmt will have more units and require more space.
At the risk of getting off topic, there's talk of a 67 being kept at Shrewsbury to act as a Thunderbird as well which would also need more space than is available at present.
In any case, one of the benefits of a massive fleet of similar units is the more efficient stabling that can take place. Instead of needing to send rakes of empty Sprinters from Crewe in the morning, with 175s going the other direction (because of Chester being set up for 175 maintenance and Crewe for Sprinters) it'll be a lot easier to keep units where they actually need to be for the next day, reducing empty milage. This will probably see stabling points re-evaluated across the entire TfW network. We're already seeing that with the discussion upthread about Llandudno Junction, with plans for units being stabled there every night (whereas at present there are two separate ECS runs down the coast every morning, with 175s from Chester and Sprinters from Crewe).
Yet more reasons why a massive order for 197s was the right choice, instead of going for a smaller fleet just for expansion on top of holding on to the older units.