Key to high performance in 3D applications is deciding what objects in the world are actually visible given the current camera position and direction.
SGI had worked on a number of projects that were intended to help the developer produce a high-quality scene graph, but none of these had become widely used for a variety of reasons.
Open Inventor was one such example, and was intended to simplify building the scene graph, but the results were not necessarily very high performance.
OpenGL Performer was a similar project that was intended to produce high-speed scenes and support very large numbers of objects in the "world", but was not particularly easy to use.
Among these were a variety of VRML tools, and a large model visualization system for CAD purposes called OpenGL Optimizer.
They had stated that the existing Cosmo work would be abandoned and that Open Inventor, Performer and OpenGL Optimizer would be re-written to be hosted on top of OGL++.
As OGL++ was intended to be a cleaned up and more flexible version of Cosmo3D, most of the Cosmo3D team started work on OGL++ and a lot of the effort was aimed at a specification and implementation that could deliver on the promise of a truly powerful yet generic scene graph.
The project appears to have been a victim of SGI's shifting priorities through this period, changing directions in order to partner with larger companies.