It's not really feature creep as much as it is implementing real ways to solve problems and satisfy features.
The features of an HMD are:
1. 3d
2. Covers user's fov
3. high def display (1080p minimum, 4k is more ideal, 8k is probably the most that could be used)
4. high refresh rate (90hz minimum, could go up to 160hz probably)
5. orientation tracking (roll/pitch/yaw)
6. position tracking (x, y and z)
7. Very low latency between movement and display update (<40ms, 20ms is ideal)
#2 isn't really attempted with the prototypes of the rift, though they have gone way passed previous releases of HMDs. The infinitieye attempts this. (Blue is the rift, yellow is the infiniteye)
#3 is only possible in the last few years primarily because of improvements from smartphone technology (Which is really the impetus for this whole VR craze last year and this year, Oculus started by Palmer dicking aroudn in his garage by taking apart smartphones and posting about it on forums). #6 is only possible atm with a solution like they have with a camera. Tracking 3d position in small movements with high accuracy is very hard. #7 is only possible with very recent displays using OLED technology, because even though you could get very quick responses from your orientation estimate and update your game engine fast you'll still have smearing and lag in the display. There's still a huge problem where Oculus has to get a vendor that can mass-produce world-class displays. Samsung blows huge money on R&D to get displays like the S4, so a small outfit like Oculus getting a matching display is non-trivial.