The North Wales mainline runs from chester to Llandudno or to Bangor. Since it has been took over by transport for Wales in the past few years it would be good to have the north Wales mainline because they are getting new trains in and upgrading a lot.
I would vote for this route either an 1980s version with Class 40s and a new 25 and maybe a new DMU (104 maybe). Or 1990s 37s and a sprinter. Would be a popular route regardless. Maybe easier to do a retro one with licensing etc
Thinking more this would give the 40/45/47 a new and authentic line to work over. Oh and the 33 too! And perhaps the 20s. New loco could be a 25 and maybe a 108 or 104 dmu which could be subbed on NTP. It's a route from Class 40 folklore being the journey of the 'Bangor'. Timescale could be tricky to get right as after the mid 80s the A55 changed the appearance of certain areas. I would set it just after the A55 was done and maybe then it would have an appeal to various eras. This could be a really good one for DTG to consider as the TS2021 version had to go off sale due to licensing (I think?) Some container wagons may be needed for freight too.