IBM in the millipede nanostorage design along with other "Frazor" nanomilling inventions essentially covered this area about 20 years ago. Indeed the tip image looks very much like the millipede thermal tip.
Although not addressed in this article or perhaps part of the NanoFrazor effort additive methods were a very early goal of these designs. Such additive systems are true 3D Printers in that they work by adding material to target surface.
Finally some methods supported and used both additive and subtractive methods. 20 years ago these systems had 2.5 angstrom resolution in all axis (imaging resolution), surface modification resolution of 2nm in X,Y and Z. They are much improved today. The machines are built and sold by a California company. The creation of these methods was done in Northern California. The earliest machines used an IBM AFM platform as a base element.
Yes, you are right. It is a subtractive process, and as I mentioned in the story, the name of the commercial version--NanoFrazor--is a play on words between the English word razor and the German word for "milling machine," frase. That said, it does sculpt 3D images of structures that can be filled in with deposition and fits in well with the other subtracive processes used in chip fabrication.
Very powerful new technology. Not to be too semantical, this sounds more like a subtractive process, where printing is an additive process. I would think it would be 3D CNC Vs. where you have it at 3D printing at the time of my writing this.