My pick for a realistic Bulgarian TSW route would be Sofia – Septemvri (around 135 km / 84 miles). It offers a great mix of intercity, regional and freight traffic, varied scenery, and is a realistic length for Train Sim World. New rolling stock: BDŽ Class 44, the classic Bulgarian electric locomotive used on both passenger and freight services. Reused assets: BR Class 47 as a Bulmarket/private freight layer (prototype-accurate) DB n-Wagen in BDŽ livery (former German coaches used in Bulgaria) Existing German freight wagons (Eaos, Falns, tank, container wagons, etc.) DTG would only need to build one new locomotive, while reusing plenty of existing assets to create a busy and varied timetable. In my opinion, this would be one of the most realistic and achievable options for a Bulgarian TSW DLC.
The Varna-Burgas line looks very scenic. Love that coastal view at sunset. Developers need to put the 'world' in Train Sim World with new routes from new countries other than Germany, UK, and USA (although, I do prefer US routes).