The suggestion is to have the user manually enter target word count values for outlining. I appreciate @ahansonauthor for articulating how he would find it helpful.
In my dream version of Aeon Timeline, there would be an integrated writing function that includes automated word counts and user-entered target word counts (the feature request of this thread), calculated at each section level. The writer would then be able to add target word counts, write the narrative, and track words written.
For nearly three years, I have been advocating for AT developers to add a writing function that integrates with AT’s narrative sections. It wouldn’t have to be nearly as robust as, say, Scrivener, but it would need to let us drag sections around (such as chapters, scenes, passages) while simultaneously repositioning them in the other narrative views (and vice versa). With such a feature, automated word counts – both target and actual – would make sense, as AT would total words at each narrative level (i.e., in my setup, Novel, Chapter, Scene, and Passage):
Chances are, a fairly basic writing editor built into AT would be enough for a novelist like me, while those who want a more complete feature set can still sync with Scrivener or Ulysses.