well its is really, they are your cad files. Shapeways will only print whats been uploaded, so if you upload OO scale that's all you get.
OK, some of the finer detail wont probably print, I think the limit of resolution with FUD is about .5mm or .3mm if your lucky, so a couple of N inches.
I guess you could make the CAD files available (to buy), so that other could tinker with them and add or subtract detail depending on their chosen scale.
The only thing I've drawn and put on Shapeways so far is a single Ground Position Signal/light in N, working on a sprue of them to make it more cost effective, and I'm also trying to get some fiber optic feeds into them.
I tend to draw full scale if i've got a proper engineering drawings to work from and then get the CAD package to scale it down to 1:148 for me.