The West of England line is a route I'd love to see, in part, in TSW. 172 miles in total, from London Waterloo to Exeter St Davids through Basingstoke, Andover, Salisbury and Yeovil to name a few. There's tons of options for routes, but main ones would be either Waterloo-Basingstoke (47 miles), Basingstoke-Salisbury (36 miles) or Yeovil Junction-Exeter St Davids (on the longer side at 50 miles). Running over former LSWR territory, and since I can't request steam routes (yet!), there has also been a fair share of diesel electric rolling stock too, with Class 33s, Class 37/4s, Class 47/4s Class 50s and tons of DMUs, not least of which included Class 158 & 159s all working at various points. As such I think it would most suit the end of BR Blue and beginning of sectorisation, with Network South East featuring prominently, with a helping of BR large logo for good measure.
.....Yes that’s a wonderful idea, please don’t forget the class 42 warships and class 47’s that also ran on this route. I would set it in the modern day with the reinstated Axminster loop and extra platform to increase the service time table. You have a good idea there.