The NMT is a livery held by a few Class 43/0s. My thought is having them on each UK route operating Test Services across the country. I personally love the Flying Bananas and I am excited for their return. For those who don't know what I mean. For the past year and a bit they have been using ex LNER and EMR 43s until the yellow ones come back, which should be soon as a recent RailAdvent article says they have passed their testing at Old Dalby. I have hopes we can see this dlc as we already have the GWR livery 43.
I agree with you we definitely need more HSTs for TSW, and hopefully now that they say sound is a priority for them we can have AP sounds for it (although I must admit the sounds we have are pretty good)