You have a really good list there but i see a gap in times and locations. You have a lot on the east coast and some in between. I would like to add anything from the TMER&L and the south shore line. I am aware of a 3d printing company that makes HO and N scale models of the north shore steel silver liners and one or two steeple cabs. The only problem I see with modeling inturban or street car lines is that it's not all that popular. So i think that make parts, motor assemblies, detail parts, decals, paints and maybe kits would be enough to hold most of us through. As MR. Bachmann would say we only put out models that would be really popular to pay for the tooling required to make the models.