It seems to me that the processing power of workstations and high end PCs is now good enough to support platform independent VR with Web style global hyperlinks. Like Tim, I believe that the way forward will naturally lead to non-proprietary VR, and think now is the time to start exploring how we can do this. A key to allowing effective platform independence is to use logical descriptions so that viewers can fill in the details according to their own rendering capabilities. As an example, you could describe a room in terms of the polygon defining the floor plan, the height of the walls, and categories for the textures of floor, walls and ceiling. Low power systems would use plain walls, saving the cost of retrieving and patterning the walls.
Fractal techniques offer interesting possibilities too.
Shared models would avoid the need to download detailed models, e.g. for wall paper, window and door fittings, chairs, tables, carpets etc. These models, by using well known names can be retrieved over the net and cached for subsequent use. The models would include hierarchical levels of detail. In addition to appearence, models could include behaviours defined by scripts, e.g. sound of a clock ticking, the way a door opens and functional calculators, radios and televisions. So far I have outline a way in which you could click on an HTML link and appear in a VR museum and wander around at will.