I only interject because I agree with Hanon. I also played Cloak of Darkness and reviewed the code.
No offense to those who like the game, but it’s not a showpiece. A showpiece is something that is outstanding. The Chapbook implementation of Cloak of Darkness is a good example of using Chapbook, but not something that creates a buzz to attract authors to the story format… which is how I interpret the term showpiece.
Good question. I have many thoughts about this, but essentially I think it needs to be something that looks and feels better than the competition. On the surface, the game needs to draw eyes and show a level of polish, but still look attainable by a novice. Maybe a collaboration with an artist is required.
Then it needs to showcase what is does best and what makes it unique. Simplicity is the key to authoring with Chapbook (because it really is so bare bones, but very capable). The basic markup implementation in Chapbook is really good too. The table/column one in particular is fantastic with only a couple of CSS styles to bring it out of the stone age. It has a good implementation of audio (something that Harlowe lacks completely). The Backstage testing environment is really good as well.
It needs to be honest, but not too honest because reading things like this in the Chapbook Guide as a reason not to use Chapbook…
You’ve invested significant time already in learning another story format. There’s nothing that Chapbook can do that other formats can’t. It may be easier to write with, depending on your point of view, but if you’ve already spent the time to learn how to write for another story format, it may not be worth the time investment.
…does itself no service whatsoever.
I wonder now if Chapbook might be the better default story format for Twine though (as much as a conflict of interest that might appear to be) because it does what it does so well that Chapbook novices can probably do what an intermediate Harlowe author can do. It’s that simple.
Harlowe can be intimidating at first, if one doesn’t know anything about programming. The Twine beginner angle is something to consider as a showpiece too. Maybe Chapbook’s Cloak of Darkness needs to elevate itself by providing the code displayed below for each passage. It’s like, own that simplicity. Showcase it. I’ve pushed Harlowe quite hard over the last 6 months or so and what I’ve discovered about Chapbook is that it embraces HTML, CSS and JavaScript better. That’s not a minor thing and something to promote with a story, as well. Also, the number of inserts and modifiers with Chapbook is surprisingly few. That’s something to admire and makes it very approachable.
I could blather on and on, but I think you know where I’m coming from. Maybe I’ll put my money where my mouth is, so to speak, and make something to draw eyes. I seem to be quite passionate about Chapbook right now, don’t I? 
As a side note, I’ve been making my own {inserts}
and [modifiers]
with custom parameters today and Chapbook’s handling of this is simply amazing. I’m actually extending the native language of Chapbook. This really excites me, but I know I’m in the minority with that take because it requires a bit of JavaScript experience. I’m probably a beginner/intermediate JavaScript guy (I look up everything online for even the simplest solution). However, my goal is to share what I learn with the community here eventually.