I suspect we're at the begining of a move of such environments onto the web.
The HTML Canvas element gets you some of the way there by providing a bitmap display. People are already building basic demos and infrastructure for 3D applications running natively in the web browser. It's a long way from simple untextured wire-frame models to WoW, but the direction is clear. Google (and many others) have already put IM into the web browser.
So, what's missing? A way for the browser to interface directly with the necessary hardware; DirectX in the browser basically, or more likely SDL. The Ajax 3D initiative have the right idea, and have an open source plugin. However, it seems that the requirement for a plugin download misses the point of the web browser as a platform. OK, so Macromedia Flash has become almost ubiquitous for a variety of content provision, but it's not really a good way forward. Despite years of Flash, Web applications didn't really take off until DHTML, XMLHttpRequest and DOM came together to form AJAX. What I think is really needed is for the browsers to offer a standardised set of APIs to Javascript for hardware; 3D accelerators, microphones, cameras and the like. Fast matrix maths libraries are probably needed too, but that shouldn't be too hard.
I'm getting a bit lost as to what the state of the art is here, YUI, GWT and OpenLaszlo look like interesting sets of libraries for building applications, but as far as I know there isn't a standardised interface to the hardware. OpenLaszlo mentions microphones, but is that only for the Flash target?
Also, in other impressive Javascript 3D nonsense, a raytracing application with simple world builder. Not quite fast enough for real-time raytraced games, but still quite a nice demo.
