Seen this mentioned quite a lot recently and I agree. The 37 could sound so much better. the Armstrong powerhouse sounds for instance there on point
New sounds usually gets released as part of a rerelease or part of the route if you look at history. Some german locos got new sounds if you bought dra. The electrostar got ap sounds when it released with bml or when sehs was extended for tsw3. You get the idea. Since it would also probably require a physics update for it to work properly instead of just replacing sounds
It wasn't a new loco dlc. It was a loco pack or gameplay pack that could be made quickly. Loco dlc would need to be brand new train which would receive more dev time and resources