I've written a couple of RSS aggregators. The main problem with RSS is that everybody thinks it's too complex, so they create a
new syndication format, thus adding to the complexity.
RSS 0.9x was really simple, just XML and a half-dozen tags. But RDF was the new hotness, so RSS 1.0 was born, built around RDF and the Semantic Web. Then Dave Winer got annoyed at the complexity, and published a slightly cleaned-up up 0.9x as 2.0. Then a bunch of other people decided that this was a mess, and so they created a new XML format called Atom, which is only slightly more complex than 0.9x/2.0. (I'm leaving out some ancient politics and oversimplifying.)
When I was an author of feed readers, the only one of these formats that ever annoyed me was RSS 1.0, because RDF requires much more than a simple XML parser. Oh, and maybe 25% of webmasters are totally incapable of generating valid XML, so you needed to tell your XML parser to use a dodgy "recovery mode".
In practice, this has very little "cognitive overhead", because you just hand a URL to a library and it figures out what parser to run.
But as usual, it looks like people are frustrated with RSS 0.9x/RSS 1.0/RSS 2.0/Atom/etc., and think that the solution is to create yet another format that does the exact same thing. I'm sure somebody out there is writing a "robust jsonfeed" parser that can handle badly-mangled invalid JSON.
In 4 years, people will be saying, "The whole RSS 0.9x/RSS 1.0/RSS 2.0/Atom/jsonfeed mess is terrible, and we need to create a simple new syndication format based on _____!"