If you never publish it, and it's never published after your death; objectively it produced no income and has a monetary value of $0.

With no offense to you or your novel; I would appraise an unpublished novel by an unknown author at something like $100, which might be too high. Some turn out to be worth much more, but most will be produce $0 or less for the author's estate.

How is that tax going to be assessed and by who? What constitutes a novel or a book over a set of well written notes? This whole idea is ludicrous, are we going to raid people's homes and audit their computers and notebooks to see if they've written anything that might be valuable? Just tax their income. We already do it.