Atlas, MTH and Lionel have several different projects going on simultaneously with just a few road names of each. That way they can reduce costs by spreading them out over multiple runs of box cars and passenger cars and doing high end, medium and low end built at the same time. Scott's builders won't work that way. They are all of the old fashioned brass project world. They charge the same for medium and low end that same as for high end even if it takes less work. Scott also spends a lot more time in China making sure that they deliver what is expected. This fubar with Atlas's warbonnet F7s would probably put Scott in bankruptcy but it is more expensive up front to spend more time in China, and still imperfect.
As for eras, read through the thread on what era folks model. Age is almost irrelevant. Folks gravitate towards the 1940-60s lessening on either side of that era. Why, I have no clue, to each his own. Many of the younger ones seem to gravitate there because of parents or grandparents or other similar early experiences. My father was a fighter pilot who played with Lionel trains like Gomez Addams and all my grand parents were gone before I was 5 or 6 so that does not apply to me.
When the SD40-2 project was suggested I thought a GP40-2 project would do better but I was ambivalent about it and the others all preferred the SDs. At least doing an SD38-2 at the same time is 90% the same as an SD40-2. Anything else requires starting from scratch so that doesn't work.
I've been lobbying for FP45s and SDP40F for years now with Scott and have already guaranteed 20 of each. But when it comes down to folks (including dealers, even when asked) emailing Scott and saying if you make FP45s I will reserve X number it hasn't hit 50, even with my 20, and less than a hundred or so keeps it away from serious contention.
