I think motion capturing interfaces are the future. It’s already seeded in gaming and entertainment. There are fidelity and resolution issues but those will resolve sooner rather than later. For true productivity, there are ergonomic issues, like supporting your arms. Trying to use a touchscreen monitor is exhausting. But there are solutions like, Nxakt’s desk mounted tracker. It could even live in the display bezel, right now Samsung puts them right on the top of the TV, like the Wii sensor.
I think there are some really interesting interaction possibilities though: sitting vs standing, arm waving vs finger wagging, using your feet, like in a car (a very complicated 3d interface). One current disconnect though is the notion of using macro and micro 3D gestures to navigate and manipulate 2D UI menus. I think a big breakthrough will be when 3d motion captured interfaces are conceived and structured in 3 dimensions. We’re all trained in 3 dimensional hierarchies so we know how to create dominant, sub-dominant, and subordinate 3D form relationships. Future UI designers will need to consider information organization in 3 dimensions, not just 2. Top to bottom, left to right, front to back, may become upper left background to lower left foreground. Who knows, maybe in the future we’ll have to print rapid prototypes of our 3D interfaces to check the ergonomics…