Recently Amazon opened it's custom 3d printed store, backed by Mixee Labs among many others. The new landing page also features actual 3d printers and accessories for them. As well software for cad and 3d printing.
Categories for 3d printed products already include: *Phone Cases *Electronic Accessories *Home Decor *Artwork *Jewelry *Toys & Games
A video report on Amazon's 3D print store: by LogicLounge