For a much very elaborate model of what I called "multidimensional writing, see Flower, I. and J. Hayes, "The Dynamics of Composing: Making Plans and Juggling Constraints." In Creative Processes in writing. Ed. L. Gregg and I. Steinberg (Hillsdale: Earlham, 1980). What they call "the cognitive model of writing" seems to me to come close to an explanation of what should all be considered when we talk about programs that are intended to foster writing:
Putting it more generally, writing interacts in important ways with long-term memory. This is something that Luhmann also realized. for him, the Zettelkasten was his secondary or long-term memory.