Can general purpose polystryene (not HIPS) be used for 3D printing?
In principle, it should work fine as a filament, since it's used extensively in the plastic extrusion industry, but I don't think you'd get great material properties out of it. ABS and HIPS incorporate polybutadiene into a graft polymer structure for a very good reason: the butadiene sections in the long molecular chains kind of "stick together" as a distinct solid phase to produce what amounts to micro-bubbles of rubber inside a matrix of hard styrene or acrylonitrile-styrene plastic. This compound microstructure is what gives HIPS and ABS favorable impact toughness and some minor flexibility.

The flexibility is important -- the stiffer a filament is, the more it will tend to warp while printing. Based on chemistry alone, I would expect styrene to be somewhat more prone to warping than ABS. And it would certainly be more brittle. So there doesn't seem to be much reason to use it as filament.

Interesting sidenote: PLA/PHA has very favorable mechanical properties because the PHA forms a very similar flexible microstructure inside the hard PLA matrix. PLA/PHA is good stuff because it mimics ABS and HIPS!