I don't like it because it uses the = symbol which seems imperative rather than declarative. (Same with HCL, it might be a nitpick but these are languages I'm going to be using all the time.)
HOCON is interesting but at first glance it seems it might be too ambiguous for my tastes, because like YAML, because it supports both js-style ("//") and shell-style ("#") comments.
JSON plus comments is beautiful because it adds minimally to an unambiguous language which lends itself to automatic formatting (stringificiation).
I'd argue that = only feels imperative if you're used to imperative languages. Prolog and Haskell, both of which focus on being declarative, also both use the equals sign.