Is it likely that Grand Central are already in talks with Hitachi about replacing their mixed fleet with IEPs? There must be huge benefits in having all the long distance operators using the same fleet and removing the diesel running under the wires?
Having ridden from Manchester to Cardiff several times when the train has been crowded I can only think it would benefit from 5 car 180s. Not to mention the improvements in reliability the fleet could benefit from having one depot look after all the Alstom Coradia fleet.
Is there enough commonality between the 180 and 175 to allow a 4 car 180 fleet and allow some 2 car 175 to become 3 car?
possiably, as angel trains own both the 175s and the 180s, but there are some differences between the untis, for example 175s have 450hp per engine and 180s have 750hp
this could be rectified by an engine swap but then it starts to get VERY VERY EXPENSIVE.
the best scenario in my opinion would be either the 180s replacing 175s, in turn replacing ATW sprinters, then cascaded to provide extra capacity on XC turbostar routes
or, as a final option, if there were to be a franchise shuffle, the cardiff-nottingham could be part of the wales and borders franchise, and ATW could then use 180s for this, and XC could keep the turbostars to strengthen birmingham-stansted services (I have taken the service a few times, enough to tell you that 2 coaches is not enough!)