All I can say is oh dear after reading the ATW website:
"As well as the physical change to your ticket, during the pilot period you will initially only be able to buy tickets for journeys on the Arriva Trains Wales network. If you require a ticket for a journey beyond our network, your conductor will advise on how to purchase a ticket for journeys beyond the Arriva Trains Wales network"
I make a fairly regular (at least twice a month) journey from an unmanned ATW valley line station that has no ticketing facilities to Bath Spa. Currently I can board the train, buy a ticket direct to Bath Spa from the guard, arrive at Cardiff Central at 22 minutes past the hour and jump on the board the half past Portsmouth Harbour service (valid connection as the minimum time at CDF is 7 minutes). Now I will not be able to do that and presumably will have to fuss about at Cardiff Central to buy a proper ticket. Useless. Do ATW actually give a damn about their passengers?
I hope GWR do not follow down the same route as I often travel from an unmanned station on this side of the bridge too!