Consider the problem that a requirement is supposed to address. Think of the most desirable solution to the problem, no matter how unrealistic it is. If the requirement doesn't allow for this solution, then it contains design assumptions that you should purge from it. For example, for ease of use requirements, imagine the user could use telepathy or psychokinesis to accomplish their goals.Sometimes what might seem like fantasy solutions are in fact feasible. Last year, I cited research into "pass-thoughts", a technology in which computers read a person's thoughts to authenticate his identity.
Now the Guardian tells us that a "team of world-leading neuroscientists has developed a powerful technique that allows them to look deep inside a person's brain and read their intentions before they act." This sort of technology opens the door to user interfaces based on reading people's minds.