Enhancing video games in real time with biofeedback data

All video games have the ability to affect a player and the result can be seen in changes of his or her heart rate, perspiration, focus or concentration. This change is a large part of what draws a person to play a game in the first place but overtime players body starts to adjust to the stimuli in the game thus decreasing the interest. What if the game could continuously adjust to players biofeedback and keep the engagement and excitement levels high longer?