Out of the places which currently have direct trains to London, which ones need them the least? This is intended as a corollary to the post on where most needs a London service. I'd say that it would probably be somewhere with a small population, far from London, with good connections to other places with more justifiable London services.
I'm not sure if GWR extending half of its Swansea to Paddington services to Carmarthen was essential or just trying to get demand ahead of Lumo. On the other hand, passenger numbers from Carmarthen are 35,000 to Swansea, 32,000 to Cardiff and 20,000 to Paddington and I doubt TfW could have provided as much extra capacity to Cardiff as the GWR services do.
I'm not sure if GWR extending half of its Swansea to Paddington services to Carmarthen was essential or just trying to get demand ahead of Lumo. On the other hand, passenger numbers from Carmarthen are 35,000 to Swansea, 32,000 to Cardiff and 20,000 to Paddington and I doubt TfW could have provided as much extra capacity to Cardiff as the GWR services do.