Let me clarify my idea, in that I was not advocating for unpowered units, but rather considering an adaptation of the business model to start offering a few select undecorated shell components produced as extras during the production run.
It seems we are at a (temporary) impasse with the SD40-2 project, which when eventually solved will rear its head again if/when the next 2nd generation diesel run is attempted. The thing with 2nd gen EMD and GE units is that so many features are similar between the models. Looking to HO scale for inspiration, companies like Cannon realized this and stepped in to offer detailed cab kits and Rail Power stepped in to offer long & short hoods. The result is that all kinds of how-to articles and books were written in the various magazines on how to kitbash these products together using Athearn or such running gear to realize museum quality plastic models. The availability of the components created the market. I know, because the money I made building and superdetailing such models for other people helped pay for my first steps of college.
My point is, looking towards the future the forecast for reservation-built 2nd gen equipment looks dicey, as evidenced by the difficulty in reaching the minimum numbers to commence production for the venerable SD40-2. It's an overconstrained problem, which is going to persist unless something changes, and therein potentially lies an opportunity. I believe there is a market for people who would buy a completed model if they knew they could also purchase extra components to kitbash it into another SD40 variant, or SD50, or whatever...and there is another segment of people with existing diesels from other manufacturers who wish they had correct cabs, and fixed pilots to the walkways (Atlas, Lionel, MTH, Weaver). Obviously the profit made on an EMD pilot/walkway assembly, or dash-2 cab or hood would be less than a completed model, but the profit margin could be considerable larger.
The million dollar question: is the market large enough to warrant an adjustment to Sunset's business model to start including a few select components for 2nd gen diesels, and would the manufacturer be open to it from a numbers standpoint? I don't know, and I'm not advocating this as the solution. A market study would have to be conducted, although it's a bit dicey because this is a departure from the norm (at least in O-scale). It works quite well in HO, but does the business model translate?
What I do know is that looking through these forums there are a lot of people (in the 3rd-Rail wishlist thread for example) wanting specific model 2nd gen diesels which are likely to never be made in O-scale out of quality plastic since even the SD40-2 project is having such difficulty. As well, there seem to be another lot of people in the 2R and 3RS community unhappy with having to cobble together solutions for correcting swinging pilots & steps on their EMD units. Perhaps the SD40-2 project is an avenue to provide solutions to these people, and if so then O-scale as a whole will benefit.
Or not, and all this stuff should just be 3D printed from Shapeways, ha! Then they make the money.