Again just being pedantic here. This thing doesn’t look or work like HTML, but it does happen to compile to it too. I find Markdown way easier to read than HTML, and I read both all day long. Maybe having two decades of experience reading HTML Zoe whatever isn’t enough to offset the superiority of this format? (No idea. I dislike JSX, and I don’t think this is actually more readable beyond cute little examples, but I might be wrong.)
All I can say is readability is subjective. Hiccup is used quite extensively with Clojure/ClojureScript. Clojure for HTML rendering and ClojureScript as an alternative to JSX for Reagent. For people that enjoy Lisps I think it's probably great, for people that don't maybe not so much.
I definitely like the lower density of text that an absence of end-tags provides.