PostScript is a well-defined, well-documented programming language. Introducing a new layer for 3D printing would be very cool, but in the end, G-code is the "native" language for most of the hobby (and maybe other) 3D printers out there.
I'm a bit conflicted. On the one hand, G-code is very compatible with the open source ethos, but on the other it's a very old standard that was originally intended for plotters. I'd love to see something better replace it that can say, use bezier curves.
Its about as close to being a "3D Postscript" as you could find these days ..