This was also a time of great experimentation to find the “perfect” freight car design. Among the interesting solutions were hopper-bottom boxcars, the wide introduction of steel cars of different design concepts, wood cars with steel frames… or tube frames, horizontal rib hopper bottom gons, the list goes on.
People tend to think that cars from that era all looked the same, and that all there was was 36 ft boxcars. Up until 1910 or so that was not the case. Most cars in 1900 were only 34 ft and a lot of 28-30 ft cars were out there. There were low side gons, high side gons, hopper bottom gons, drop bottom gons, side door gons. About 25% or so of the freight cars had doors that opened to the left, not the right and maybe 10-15% of the boxcars had plug doors (the majority of PRR boxcar designs in the 1890-1910 era had plug doors.) then ther were the buggy and furntiurer cars, the turn of the century "high cubes’ , some as long as 50 ft.
Rather than just the 36 ft reefer there were a myriad of reefer designs in lengths from 30 ft to 36 ft with single hatches on the ends, hatches in the center of the car, hatches down the center line, hatches in the ends, bunkers above the roof, under the roof, at the ends of the cars.
Stock cars had any number of designs, some had doors near the ends some doors in the center and a wide variety of trussworks in the sides.
Its just too bad none of the major manufacturers have supported the possibilities.
I think the other posters have pretty well covered my opinions on typical model railroads and under represented themes, so I’ll offer one that I think would be unusual and challenging:
The solid rocket boosters for the space shuttle are/were manufactured near Promontory, Utah and shipped via rail in large segments to Kennedy Space Center. There are special loading/unloading facilities and special rail cars. In addition, the rail cars and re-usable rocket parts are refurbished at the Freeport Center in Clearfield, Utah.
Since the entire shuttle program is not classified, most of the information about construction of the boosters and shipping is available and the models could be very interesting.
I used to work as a training specialist for the company that manufactures the boosters. As such, I have some familiarity with nearly every aspect of the manufacturing and processes. For the contemporary era modeler who doesn’t mind doing some research and a lot of scratch building, I think it could be a great theme.
Ironrooster had the answer i liked the most. Something seen quite a bit in 3 rail that I don’t like but I do like all layouts is elevated track up on stilts. I realise that there are prototypes for this but the real reason is more track in the same space without hiding the track below.