To be perfectly clear: the only reason anyone should use RSS in new development is podcasts.
I'm personally a little unconvinced by jsonfeed too which is mentioned in later chapters, but I have to say I'd go all in on it iff it allowed us to free ourselves of RSS.
I disagree with the reasoning, because Atom is every bit as widely supported outside podcasting, and RSS is more painful to generate, requiring special-purpose date formatting rather than using the standard format that your library already supports, and requiring foolish duplication (things like description versus content:encoded) to obtain almost reliable results due to some of its underspecified or unspecified areas causing genuine pain for authors and clients alike, and simply not representing the right semantics. Atom is much more dependable and harder to mess up, and the sensible choice to implement as a feed producer, except (as mentioned) in podcasting where Apple froze it out.
For just about any other purpose, I’d say you want RSS or Atom anyway, and supporting multiple formats is actively undesirable because it complicates feed selection, so don’t even touch JSON Feed.