In a fit of autism I decided to try and identify the passenger carriages that appear in the 3.1 teaser. I couldn't find an exact model but I will say that they look very German, which would match up with the red wheels you can sort of make out on the tender. As for the period, it could be anywhere from the 1930s onward, but I'd lean towards the latter half of the century.

This could also all be meaningless and the artist just drew a generic train (the cars do look similar to ones I saw in pictures of Chinese railways), but I thought I'd report my findings here. Maybe someone could find an actual train autist to investigate further.