One of the big differences between Oculus and Valve's philosophies is that the latter believes that there must be a 1:1 correspondence between motion in the virtual world and the real one. No doing so kills presence and causes the nausea that people talk about. Having spent a fair bit of time in an Oculus DK2 I couldn't agree more.

Unfortunately, this kiboshes treadmills and things like the Virtuix Omni. At least until we manage to fool the vestibular system as well as we can the eyes.