One of the largest expansions of the VR market in add-ons will be Haptic input from a multitude of devices.
Well, Sony is one step closer with a Haptic Glove
Patents 14/517733, 14/517741, and 14/503275
It might be wise to note that Sony has made many patents on a VR HMD and not to put to much into and one patent listing when trying to guess the final product if it ever is produced. It does show that they are doing R&D in this sector. They are not alone.
It’s going to be hard to beat LeapMotion style virtually wireless hand tracking camera system.