Wouldn't Swansea Parkway be more of a connection into Swansea by bus off the train using the District Line? I'd imagine it would see a major amount of use, traffic in Swansea can be frustrating as can parking. Depending on its location, it would have the potential to bring in business from many surrounding towns and villages.
Say you're going from Pontardawe, not too many miles north of Swansea, and you want to travel on a train and you either don't drive or you can but you'd prefer to use public transport (so you can consume something alcoholic on the journey for example). The most logical choice, from what I can see, is a bus to Swansea then onto the train. That journey into Swansea can take a while!
Similar could apply from places like Loughor and Gowerton, or Bynea, Pontarddulais and many more. A drive to the Parkway station would be potentially much more welcoming than the drive into Swansea, finding a parking spot, paying for that and getting on the train.