The movie "Gamer" has a concept that is quite intriguing. As a player you control the actions of another human being. Without going into the plot of the movie, I'll attempt to explain the controls or UI.
The main character in the game(Gerard Butler) is being control in a real life "war game". The player is sitting in his room surrounded by tv screens 360 degrees around him and above him. His bodily actions control Gerard Butlers character within the game. I tried to find images online of the kid in his room standing up with his arms in a "gun shaped position" playing the game, but couldn't come up with any. A youtube search for "Gamer movie" may show something(I'm at work, no youtube allowed..shhh!) It is like Microsoft Kinect on super steroids!
There is another part of the plot where a man controls a woman in a Sims like surrounding, however it was in real life. The woman who was being controlled would actually "go to work" where she would then be connected to her controller. The controller could then tell her to walk up to people to talk, act crazy etc. Pretty much like Sims... In this case, the controller(man) would wear like goggles on his face, to see, but the control was through his thoughts and voice.
In both cases, the character that was being played was controlled by thought(?), speech and action. The UI was almost invisible at play time or when they started the game. But, in certain scenes, you would see the player setting up the game and they would use full body actions to slide things across the screen, etc., like Minority Report.
The concept of making the UI as transparent as possible is the goal we may be working towards.