Welcome to the forums, I hope you enjoy your stay here So, you are getting confused between routes here, the North Wales Coastal is the route I think you mean as that runs between Crewe and Holyhead (that I recently suggested myself) as the South Wales Coastal is the line between Cardiff and Swansea
As I said in traingeek's great suggestion the north welsh coast is a route that would be much better done in the early 80s.
Please research your routes before suggesting them This is NOT the South Wales line, or even in South Wales... A decent enough route to have built, but you might as well just say "Any route in Britain" and leave it at that https://forums.dovetailgames.com/threads/north-wales-coastal-crewe-holyhead.70536/ That's a decent proposal for the same route
Welcome to the forums mate. Usually suggestions have a bit more detail and info associated with them and are looked more by the community of this forum. If you want a idea for another way on how to make a suggestion you can look at my suggestion (Train Sim World 3 - North Wales (cymru) Coast Line Mid 1980s | Dovetail Games Forums) of the same route set in the mid 80s as a template or a reference for this or future suggestions by you.
Crewe to Holyhead would mean the North Wales coast can you re edit your title if possible. I have suggested this route myself from Chester to Holyhead so it would get my vote either modern day or 80's or 90's .possibly The length would be 105 miles so probably Dovetail wouldn't bother adding all the route Maybe it would be too much work for the full route. But it's great that you suggested it ,we could do with a Welsh route included in the game. Thanks for your idea hopefully we can get the North Wales route added if enough people are interested