I had a quick talk with Kermit Woodall at a recent show when someone was asking about a strange connector on a GVP accelerator. It turns out it was a connector for an in-developement version of the EGS-Spectrum.
He was talking about a Cybergraphx-like system that GVP was developing that was really fast, and could amazing things that CGX or P96 still can't do. (Something like being able to promote screens to a picture-in-picture display, or display many screens simultaneouslyon one monitor, or promote screens in a video-wall.) Unfortunatly GVP tanked before this came out.
Anyway, after talking, I enquired about EGS and he said that's different. EGS is a set of graphic libraries that is similar to the amiga's own, it has it's own windows, gadgets, etc. In order for software to use EGS, it has to be compiled to use those EGS libraries. So CGX software won't run on an EGS system (unless it also has CGX).