I see this as a good way to do a few things:
Couplers, trucks and other detail parts in natural rust color.
Ties in natural color.
Engine and car shells in a base color similar to the intended paint color - this would reduce the visibility of possible paint chips.
Engine and car shells in a natural rust color - this could open up interesting weathering ideas.
Small, thin details in an opaque color.
But my biggest hope is that the surface detail is better than FUD or whatever they call it now.