A Sunset quality RS-3 would be nice.
I would dearly love to see a SW1500, especially if painted in the Manufacturers Rwy scheme.
I'd also love to see a Alco C-415--I'd think SP and BN modelers would provide some volume.
Finally (and I'm not holding my breath for any of these to be made), Sunset could do On30 modelers a huge favor and release a well done 8-18C 4-4-0. Eureka & Palisade #4 and North Pacific Coast #12 Sonoma are two surviving examples.
Jeff C