Does this require you to invent 3D user
interfaces?
Yes, and no. Good 2D interfaces are hard - in part due to the limited
pixel space and the necessity for abstraction to represent complex
concepts.
3D gives you much more latitude in your designs, but is hard to do well
for similar reasons and, in large part, for lack of a large common
vocabulary of 3D interaction designs.
Let's see what we can do about providing the basic building blocks, so
you can go out and start building from a common interaction vocabulary.
Let's get concrete about a few of the building blocks which are
available.