I think a line in the Scottish Highlands should be added with the potentially the class 156, the class 43 intercity and the 45157 Jacobite Express. With the Glenfinnan Viaduct.
DTG are no longer doing steam traction and seems no third parties are interested. This route has been suggested many times and in various eras. The problem for DTG is that despite the magnificent scenery, traffic levels are really too low to build a timetable that will give more than a few hours gameplay. Even going back to the 70’s when there was loads of freight at Corpach wouldn’t add much. So likely to fail at least some of DTG’s LAMPOIL assessment process.