You know, a "randomize me" choice that was fair (that is to say, not obviously offloading the worst stuff or stinting on portions or giving you the same "random" thing every time) is something I might actually use for meals if I could.
There's this tea place online I buy tea from, what-cha.com , and they have a "mystery" tea section that's really awesome for trying out new stuff. And the reason it works is because the "mystery teas" are still decent quality.
But I imagine fast food places don't implement this because some jerk would harass the workers over it.