What’s so bad about HTML Comments as structure?

I’ve been getting a lot of traffic recently, due to my detailed critiques of some of the choices being made by the developers of WordPress’s new Gutenberg editor. One point I keep mentioning is the problem with storing post structure as HTML comments. It’s been brought to my attention that I often gloss over this issue with a general dismissal, without detailing why I am so dead set against it. To me, a lot of these issues seem obvious, but to others they might not. I’ve got a unique blend of formal Computer Science training and in-the-trenches work on both Enterprise and OSS projects, that may lend a different viewpoint than most. To that end, I wanted to put out a hyper-focused post, to explain all of the issues I see with the new WP Post Grammar structure.
Track Record
This one is a relatively basic issue. WP Post Grammar is new, and while it is a formal grammar, it hasn’t undergone real-world testing beyond what is supported by the currently limited API. As soon as Gutenberg is released, people will start abusing it in ways the core team hasn’t expected. With bespoke systems like wpautop and shortcodes, this kind of abuse lead to exposing serious
Source: https://managewp.org/articles/16186/what-s-so-bad-about-html-comments-as-structure

source https://williechiu40.wordpress.com/2017/09/25/whats-so-bad-about-html-comments-as-structure/