From what I hear this service will be an extension of the Pembroke Dock - Cardiff swanline stopping service, which may not actually be an attractive proposition for many travellers, if for example, it would still be quicker to get a fast service from Swansea - Cardiff and connect to GWR there.
From a time saving perspective it would probably be better to use to Milford Haven/Fishguard main stations only service, of which there are currently:
- Milford Haven - Cardiff - x6, departing 0554, 1200, 1400, 1655, 1800, 2038,
- Fishguard Harbour - Cardiff - x2 departing 1600 & 2146, with others just going to Carmarthen but could be extended
The journey time of both is approx 2h45mins.
Most of these services have layover time in Cardiff/Canton Depot of at least 1 hour, so would make fleet usage more efficient by keeping them off Depot during the day.
There are currently x7 Pembroke Dock - Cardiff services with journey time of approx 3hr30 mins, with 10-15 minute layover at Cardiff Central before returning, so no slack in the schedules.
It would be interesting to see what connection options this service would open up. It could boost tourism to West Wales for people from Bristol/South East Wales having direct links to the West, and vice versa opens up direct links to central Bristol from West Wales as well as connections to the Southwest.