I think everything apps are actually sort of a logical conclusion for HCI. The one that my job uses has redundancies everywhere, i.e. a global search bar, multiple links to the same page spread across the website, etc. It's very disorganized, but I've also found it to be strangely useful.

Maybe take this with a grain of salt but when I'm drunk I hate backtracking through UIs and being hampered by organization. I think an everything app would be useful in that case. And in the same vein as "the average human has less than two arms", I feel like the average end user is basically drunk.