It would be cool to see a modern german branch line as we only have the niddertalbahn at this moment, which plays in the 90s, and also a modern german DMU, we do not have any (Consider the 642 isnt that young anymore)! The Oberbergische Bahn (RB25) serves several stops in a beautiful landscape between hills and valleys. Starting at cologne, you serve some S-Bahn Stops until Frankfurter Str.. After navigating through Rösrath, you find yourself in a hilly nature. It has a length of 97kms, since its quite long and could decrease performance, Köln - Gummersbach should be enough, with only 59kms. You could add easter eggs into it, for example the museum at Dieringhausen. BR620/622 are used on this line, single and double units.
nice one, but IMHO, I would prefer a modern and fast diesel loco like BR 246, a fast mainline diesel capable of 160 kph, but this one seems nice tho... also 642 would use updating, since it is reportedly slower to accelerate than IRL, where it is known for very solid speeding up and being generally very nimble
