Sitting down and playing with "what needs to be in the box" for OpenGLContext 3.0 (the most boring working title I can come up with). Time constraints suggest I'll have to do a migration rather than a re-implementation, so the name is probably apt. The GUI-library integration is fine, the scenegraph engine, node-paths, matrix calculation, etc. are all working and effective.
What's left is the fun stuff. What features would you want in a rendering engine these days; basics such as shadows, mirrors, and transparency are obvious. Geometry types? Polygonal, obviously, but what about subdivision surfaces, NURBs, etc are they optional, or a requirement? Terrain/environment support; do I need portals, ROAM, Octree/BSP, or just load the whole thing up and trust to frustum culling? What about backgrounds; sky-boxes, procedural clouds/terrain, panoramic support? Interaction; avatars, collision detection, mouse and keyboard based movement, but what about editing controls?
Most of those features are pretty far off in terms of implementation. The idea of looking at what needs to be in the box eventually is to have in mind what might come so that choices now won't preclude later implementations. Anyway, for now the boys are up, so I'll have to leave all the dreaming for another day.