I'm probably late to the party here but I just stumbled across a new-to-me S scale manufacturer Concept Models.
They also deal in HO scale but show lots of promise for S scale modelers. It looks like the cars are in kit form. One of their models is available and it appears to be completed less couplers:
There are many other types of cars on the website that look like they would need wide radius curves to operate.
Kit cars aren't my thing but to the scale modeler these cars would add some exotic S scale additions to the layout.
Mark
