The Web3D Consortium lists four things: business, education, entertainment, and 'multiuser' (the latter being Web3D Consortium—speak for virtual communities). I'm going to break it down more.

Medical. The quiet giant of almost any content market, medical training, medical B2B, and medical B2C will be big business as long as the general public is afraid of death (this will probably continue for at least a few more years). 3D could have a massive impact on medical communications, distributed training, marketing, and more.

Should you add streaming 3D to your list of streaming deliverables? Sure. There's a lot to learn. Starting now will prepare you for the 3D expansion that is, at this point, inevitable. The key is to remain modular. It's too early to commit to any single 3D player right now, and you really don't have to choose. Most of your development time will lie in creating content, not getting it to the Web.