Eye tracking technology already exists and it's pretty likely to make it into the next generation of HMDs (think small IR camera inside the headset recording your eyeballs). Facial expression tracking is doable as well: https://www.technologyreview.com/s/537566/oculus-rift-hack-t...

If technology comes far enough that telepresence is preferred to on-site, I think it would be pretty trivial to replace the headset with whatever is behind them in VR

You get to see their fun avatar! That will never get old.