Here's a suggestion for the upcoming West Cornwall Local DLC. First, some context: I was a bit disappointed not to see a HST included with the route. It felt like a dead-ringer, considering it's been in TSW since GWE was put out. Having an older version of the HST in TSW is a hope of mine and I thought WCL would make it a reality. However, there's still this possibility. Having it as an add-on would be nice, as I think the HST is a legendary train (why it wasn't in Diesel Legends, I have no idea). With WCL running from Penzance to St Austell rather than Truro, we now have more space to open up the taps on the HST. Because I'm no expert on exactly how often the HST was used along this route or how much it could be used, I would understand if it couldn't be added because of a lack of potential. However, an authentic and original Valenta-engined HST would be an insta-buy for many HST fans and may bring extra interest in WCL. Disclaimer: I don't own these images And that's about everything. I'll edit in more info from comments from the experts
From what I've read the HST at the time was used about once an hour in the peak with less services later on in the day, the cornish railway timetable was slashed in the 80s and 90s to the point that part of the line was reduced from dual to single line running to save costs, only being reinstated around the late 90s So yes the HST is iconic and ran down to Penzance, but maybe not as often as people would like to think. If the line from Plymouth up towards Bristol was modelled then the HST would absolutely be a necessity to make the line authentic (let alone up from Bristol)