Expanding thoughts on the practicality of the Wii U controller for MMOGs in the post comments, the presence of a microphone suggested the possibility of allowing voice commands, though as Melmoth pointed out shouting “bugger this!” in frustration at a boss fight might not quite have the intended result.
Mechanisms such as Rage for Warriors in World of Warcraft and Fury for Brutes in City of Heroes build up a bar as you attack or are attacked to power further abilities, but a bar on screen is a rather abstract representation of furious rage. How about if they were powered by the *actual* anger of the player, with your attacks doing more damage the louder you shouted, and taunts depending on the frequency and strength of swearing employed? Accelerometers offer further opportunities for capturing the force with which the controller is hurled aside at the peak of annoyance.
This would give the perfect difficulty scaling system. Rather than, as at present, repeated failures resulting in a downward spiral of anger, recrimination, impotent ranting on voice chat and less focus on the game precisely when most needed, the fury of the player will instead power up their character to unprecedented levels until they’re capable of one-shotting any boss.
Course it would need recalibrating for individual players, otherwise some people would be massively overpowered all the time…