Any psychologist can tell you, it's difficult to understand what people are really thinking. Sure there are non-leading surveys, and GSR dongles, and eye-tracking, and study deception, but these are all still guided behaviors and can be translated in different ways.
Psych is still a relatively young discipline, compared to other soft and hard sciences. Thus, there are bound to be some growing pains. User research is an even younger field, and as I get more engrossed, I start to identify some of the behavioral measurement issues in UR that psych once (and might still kinda) faced.
So what's the point of bringing this up?
I am convinced there is more to UR than is currently available. Web/game/app analytics are getting better everyday. There is no longer a need to overtly ask a user/participant what they are doing because their behaviors can be tracked with minimal, if any, interference. Biometrics and VR in gaming is starting to poke its head out to gather even more data on what players are doing and how they are physically responded to stimuli. Consumer electronics that track physical activity and sleep patterns are getting cheaper and easier to use. Mountains of data about my body please!
The data is out there. The problem is making sense of it all. The even bigger problem is making sure the sense that is made of the data is actually correct. UR has the tools in place, it just a matter of genuinely understanding what a user is thinking and feeling when interpreting these data since users/participants don't always know what they're thinking or why.