You assume that keystrokes are independent from each other. They aren't.

somebody knew absolutely everything about the state you were in when typing they could reconstruct you just from this.

They don't.

You probably get a lot more relevant information about yourself by using various QS tools like MyBasis. I personally didn't get a MyBasis but I have preordered Angel.

My Anki review data pile, produces a bunch of information about my brain state that's of much higher quality than random keyboard typing.

Anki data in addition to heart rate data from Angel tells you which Anki cards produced hypothalamic reactions.