I worked for over 35 years in the printing industry, and saw many changes in technology over the years. (From letterpress printing, to web offset printing of telephone directories). The most advance system I personally worked with, was a computer-controlled registration system. (CCR for short). It involves the use of registration dots which were printed onto the web travelling at speeds up to 2500 feet per minute, for each of the four process colors used. CMYK, a television camera was mounted onto a linear rail system, which allowed the camera to travel across the web, driven by a servo motor and toothed belt. The camera would make a scan across the moving web, under computer control and photograph the programmed location of the registration dots on the web itself. A specific pattern arrangement of the dots (I.E. the distance from Cyan to the Magenta, Cyan to the Yellow, Cyan to the Black, and so on, relative to each of the 4 colors) was the "Target" to be maintained by the CCR. This was accomplished, by electric servos, which manipulated the registration of the plate cylinders for each color on the press itself. To be sure, the system was a multi-million $ system. And further improvements which included a computer controlled ink density scanner and closed loop control (to control dot gain) made that particular printing press the most advanced system I ever worked on. So, I can see where it could be possible to develop a similar application for what you are trying to do. However, I don't think that Mach3 (as it is) could accommodate such a system, since it would require constant re-writing of the G code during program execution.