UPDATE (9-22-15): Someone on youtube has built one! Video at the bottom.
UPDATE: David has a great write-up on spray-paint-lasering PCBs:
@SUF and @Radu Motisan found these prebuilt laser-engravers (photo/links below) while looking into using laser for PCB-etching. The idea being: Spraypaint the PCB, then etch the paint away with a laser. Something David (who's not showing up in the dropdown list: https://hackaday.io/hacker/15795) is currently doing with CO2 lasers. The jury's out on whether these lasers would be powerful enough to burn away the spraypaint, but maybe a different type of paint...?
These are the laser-engravers:
They look suspiciously like CD/DVD mechanisms!
This ain't mine, but it's cool to see it in action!