Game developers could feature maps, weapons and character models on their websites instead of just screenshots, concept art and videos. It would be a nice addition to product sampling.
I also see the possibility of people being able to record a game where it makes an explorable 3D scene of a previously played match. This already takes place in Halo 3 and a few other titles, but now we can share the content on the web for everyone to see.
People can also make 3D avatars (and no, I don't mean little people that walk around). Forums use animated GIFs and animated PNGs that are often simple logos or symbols. Any video or animated image of a simple symbol or logo uses way more data than an animated 3D object of the same thing (in most cases).
Last but not least, making all web pages 3D. PHPBB could make it so threads can be navigated with arrows keys or the mouse like you were floating through the forum as a landscape. A forum could have rings of threads and for every thread with MORE threads, more rings. Then when you get down to the posts, you could click to load the previous page or the next page and it would roll out like a scroll.
I hope I didn't confuse anyone with the last two paragraphs (I confuse people from time to time). If it needs explaining and sketches, then email me: [email protected].
I'm anticipating there will be a lot of great things we never imagined before. It isn't always about improvement of the web's functionality either. Even the feel and means of navigation can go beyond our simple imaginations.