I really think the 171 class should be apart of the east coastway and the Ashford international to Eastbourne route.
AP has included the 171 in its 170/171 pack. I would not mind seeing a route using it if DTG were able to get access to it for a new model, or at the very least modify their own 170. Also, isn't Eastbourne represented in TSW2?
Thinking about it, Ashford to Eastbourne is actually an ideal route; you've got a mix of double track and single track diesel and electric services, depots at Ashford and St leonards, and large termini at both ends of the route (and the middle if you count Hastings). Scenic with a mix of marshland, countryside and seaside locations (the track hugging the coast near Bexhill is particularly nice). Length is about 50 miles (so not too long or too short) and drive time is about an hour. Rolling stock is the Class 375, 377 and 171 (all of which already feature on TS) and the TOCs are Southern and Southeastern (so presumably no licensing hurdles). Perfect for the AP Class 205 and 411 if backdated as well
As Hastings is being mentioned here there is a very good route from the link below, Tonbridge-Hastings. https://backdatedtrainsim.weebly.com/route-downloads.html AS TSW has a Brighton-Eastbourne route DTG could extend that to Hastings or even Ashford for TS. At least they have some of the groundwork.