So I like to distance this type of input from the term "motion controls" because of the kind of ignorant connotation it seems to have among some, so I call it positional tracking. And the cool thing about positional tracking is that, regardless of how you derive your position, in 3D space, it is always defined in the same way - as a matrix. What this means is there is a fundamental degree of interoperability among all devices that can track position accurately.
Realistically, there are only 3 ways currently correctly track position in 3D space, and each has it's draw back. You can use magnetic induction, as the hydras and STEMs do, you can use inside-out positional tracking, as the wiimote does, or you can use outside-in positional tracking, as the rift and playstation move does.
Magnetic induction tracking has a lot of problems with interference and accuracy, becoming logarithmicly less accurate as you step away from a central base. We use this, obviously, to track in HL2VR. As the "worst" tracking solution of the 3, I think it's still pretty good, and I think the STEMs will be much better. But I think inside-out positional tracking is the single-best solution available.
Outside-in positional tracking is subject to occlusion, meaning you can get in between the camera and the object being tracked, and it will lose position. Inside-out positional tracking mounts the camera on your headset, so it is always within your range of vision. The old limitation on inside-out tracking was that you needed external landmarks to track - the wii used a sensor bar, and valve was using QR codes taped to walls at dev days. Valve's headset uses a new technology they've created called Lighthouse - it is dedicated positional tracking hardware. Lighthouse sprays IR light across the room using a laser and prism, which is invisible to our eye. The cameras on their headset, however, can see these dots and use them to track in absolute, 1:1 accuracy anywhere in the room.
It hasn't been revealed yet, but their controllers track using the same thing. They are inside-out tracking, they never lose orientation. This is the single best tracking solution possible, so I'm pretty excited about it.
Regardless, back to my original point, they all boil down to the same information in the end. So you don't have to worry about competing standards - the way we are using positional tracking is the way all projects will eventually use it. It's inevitable. With Move being a big thing for morpheus, Sixense about to ship the STEMs, and valve packing in a positional tracking system, it's safe to say that, if you're developing for VR, it won't be unreasonable to assume you can track your user's limbs
