Victoria to Dover via Chatham would be a decent route, but of course NOT highspeed as it goes via Chatham Mainline. Might be a bit long (50 miles is around about the max route limit they develop at the moment) and uses the electrostars which we've had a fair few runs for recently (SEHS, BML...)
Plus until the save game becomes more reliable (TSW3?!), that’s about the most you could push a run without having to save and return later, for those of us who only get an hour or so at a time on the PC.
They still need to meet deadlines unfortunately. Also like it was mentioned the save game is broken. If you save and load, it causes a lot of issues so unless you're going to do a run in one sitting it's not a viable option.
Routes take a while to make since most things are placed by hand. Deadlines, route complexity, time to finish a run also are a reason. There are routes that are longer than 50 miles but not that many.
Are you trying to propose the Chatham main line a train simulator classic for TSW2. Railtour train Class 71 electric with Golden Arrow sleeper