The Brightline in Miami Florida seems like a good place to start since they are actually expanding it in the future it would have many expansion possibilities. The Fort Lauderdale to Miami line seems to be in the range for the length of routes that DTG does. Here’s a pic. There’s good possibilities for extra dlc and there’s also freight that runs along these lines. An international route I would suggest is maybe any where mountainous or hilly in India. Because there are a lot of rural areas allowing you to see the natural scenery. The old routes would give users a challenge in navigating steep grades. It would be similar to the Northern Trans Pennie DLC but India still uses rolling stock that looks similar and hasn’t upgraded much of its tracks yet. I feel like both routes go in a direction that DTG hasn’t gone yet and that’s replicating modern up-to date routes. However the way the DLC could be made could feed off the spirit of Rapid Transit and Northern Trans Pennie and maybe even Main Spessart Bahn.