This tool could simplify cognitive load in two ways. One is by helping you visualize a given stream - untangling the mess of text, data, and what-have-you, perhaps scanning for known headers and letting you drill down on individual components.
Another is by helping you composite functions to operate on data. Say I have a video stream, and I want to extract every third frame, scale and quantize them, and convert to an animated gif. Quick, what's the syntax? Yargh, man page hell. 20 minutes later, I've got it, but it wasn't any fun, and some of the commands weren't stdout-friendly so I couldn't apply pipes that way I wanted.
I'd love a better way to explore functions available to me perhaps based on data type (e.g. Image* -> Image) and even browse and preview user-contributed transformations. There was a Haskell shell that went in this direction, although Haskell is sort of the opposite of UNIX so not sure this is part of the plan ;)