Can you walk around, walk away and come back? How much movement is allowed before experience breaks down? This is the major difference between VR devices like Occulus/Cardboard vs Hololens.
Do you happen to know the limitation they are getting around requiring cables? I can only imagine in the future it will be wireless. Not that I think I could wait that long to try VR, just curious :)
Bandwidth, power, weight, cost, combination of all?
All of those things. With current headsets you'd need to losslessly stream 1200p video at 90fps which is a lot of bandwidth and those numbers are only going to increase. It also has to be very low latency and not skip/stutter to avoid motion sickness. Hopefully we'll see it in consumer headsets in the next 5 years.