If you look at the current state of VR, neuroscience and prosthetics, you'll notice just how far off we are from realizing a fantasy device like the Nerve Gear. In fact I'd dare say that the headset as presented in the anime, which you just put on your head, is physically impossible - it would definitely take some invasive surgery to capture any and all instructions from the brain related to motion and speech (with good accuracy) while also preventing them from reaching your real limbs. The kind of surgery that may paralyze or kill a person.