alt Hacker NewsI'm not a fan of these custom elements. Unless you do something really interactive, dynamic and reusable (an element with complex behavior), I don't think it's worth to use them. The SEO / accessibility becomes more challenging. Also, worth to noting, web components require JS, so they are not pure "CSS" web components. Web components are useful for isolation, when used with shadow DOM.
Using custom elements as the article suggests doesn't require JavaScript, so they are "pure" HTML and CSS (though whether they count as "web components" is up to you). More to the point, all of the technologies that the term "web components" includes — custom elements, <template> tags, shadow DOM — can be used without JavaScript.
<div> and <span> are semantically neutral, so I'm not sure what SEO and accessibility challenges custom elements would introduce?