The common use I'm referring to is similar to the OP, which is using it as a framework for assessing risk. In particular, aligning a team on the "known unknowns" is critical to building the confidence and alignment needed as a group to be able to deal with unquantifiable/inestimable risk.
I just took a look at that wiki article for Rumsfeld's usage of the "There are unknown unknowns" and I had no idea that he barrowed this phrase to frame his arguments and I was only familiar with that context, unfortunately.
