I’d also add Google dropping reader and trying to force open web content into various proprietary schemes. Atom’s many improvements over RSS didn’t matter as much when the oxygen was getting sucked out of the room and few people were investing more time in feeds.
IIRC RSS was not originally an XML document, so CDATA tags (to prevent XSS) didn't work; and the issue remains with content syndication: feed elements should somehow HTML escape their content to prevent XSS (arbitrary JS on a different Origin)
The whole internet was broken, and RSS helped us realize it: the one-way, one-time syndication advantage.
These days it's all about https://schema.org/CreativeWork JSON-LD instead of RDFa, which you can try to sanitize with Mozilla/bleach like arbitrary HTML in comments on the page.
AFAIK RDF Site Summary (the original meaning of "RSS") used XML from the start¹. You may be thinking of spiritual predecessors like the Apple-developed MCF².
It really amused me that people think "RDF never caught on" when it is the basis of so many major standards such as RSS, Adobe's XMP metadata, and, I just found out, ActivityPub.
I was working on a standards committee for years and made the discovery that you can turn most XML Schema Definitions into an OWL ontologies and thus automatically transform conforming XML documents into RDF documents.
(People had attempted this before but all the systems I saw were lossy or didn't make valid and decidable ontologies.)
For better and worse my write up[ is about to become one of those ISO standard documents that costs 166 swiss franc but it looks like I'll get the opportunity to apply this method to a major financial standard and release the software that does it as open source.
I'd contrast that to the truly awful RDF/XML spec where people never really understood where the XML stopped and the RDF began. It turned a lot of people off to RDF and people never got to see how easy it is with Turtle. Unfortunately JSON-LD hasn't got the love it deserves because it fixes most of the major problems with JSONs except for the lack of /* comments */ and you can frequently add a touch of JSON-LD to a JSON document you find on the street and get instant RDF you can query w/ SPARQL.
It looks like the W3C has started the process of a SPARQL 1.2 spec which could be a very good thing if it catches up with what is possible w/ document database query languages like N1QL, AQL and such.
> It really amused me that people think "RDF never caught on" when it is the basis of so many major standards such as RSS, Adobe's XMP metadata, and, I just found out, ActivityPub.
What does it mean to have caught on or not, though? How many RSS, XMP, ActivityPub implementations are actually considering things as triples and not just considering parent-child relationships within the XML tree?
Pretty sure I can remember the actionscript XML parser failing on RSS in like 2000 and the feed was to spec.
With that app, at least, I don't remember trying to just include RSS feed elements in HTML4 or XHTML; that app tried to parse the RSS and failed, it wasn't copying the feed elements without escaping href=javascript: links etc.
Note that it's an XML file with <channel> elements, which contain <item> elements, which contain <title>, <link>, and <description> elements. Pretty familiar, no?
Dave famously introduced the <enclosure> element in 2001. This has made a lot of people very happy and has been widely regarded as a good move. http://backend.userland.com/rss092
Or perhaps having at six year head start (RSS 0.90, 1999; Atom, 2005) and having it compound.
This includes podcasting, as the term was coined in 2004, but which was happening even before that (and before Atom was finalized):
* https://en.wikipedia.org/wiki/Podcast#Etymology
First mover advantage, leading to network effects, can be a thing.