The upcoming GSPdf version can be used seamlessly to do Print Preview in GNUstep. The provision to do that has long been in GNUstep's printing code, but no application exploited it.
GSPdf is undergoing quite some restructuring and is now a true document-based application. This allows it to register properly for the post script viewing task. Activationg GhostScript's anti-aliasing is supported too (look at the screenshot, where Graphos itself is running without).
GSPdf is an interface to ghostscript as gv is, so the displayed quality should remain the same.