> Need to continually poll servers for updates? Miss.
The point of these syndication formats (RSS, Atom, now this) was always to act as the "I'm a static site and webhooks don't exist, so poll me" equivalent of webhooks. These "pretending to be webooks" were supposed to hook into a whole ecosystem of syndication middleware that turned the feeds into things like emails.
And that—the output-products of the middleware—was what people were supposed to consume, and what sites were meant to offer people to consume. The feed, as originally designed, was not intended for client consumption. That's why the whole model we have today, where millions of "feed-reader" clients poll these little websites that could never stand up to that load, seems so silly: it wasn't supposed to be the model. RSS feeds were supposed to be a way for static-ish content to "talk to" servers that would do the syndicating for them; not a format for clients to receive notifications in.
(And we already had a format for clients to receive notifications in: MIME email. There's no reason you can't add another MIME format beyond text/plain and text/html; and there's no reason you can't create an IMAP "feed-reader" that just filters your inbox to display only the messages containing application/rss+xml representations, and set up your regular inbox to filter out those same messages. And some messages would contain both representations, so you'd see e.g. newsletters as both text in your email client and as links in your feed client, and archiving them in one would do the same in the other, since they're the same message.)
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The big problem I have with feeds (besides that people are using them wrong, as above) is that they have no "control-channel events" to notify a feed-consumer of something like e.g. the feed relocating to a new URL.
Right now, many feeds I follow just die, never adding a new feed item, and the reason for that is that, unbeknownst to me, the final item in the feed (that I never saw because it rotted away after 30 days, or because I "declared inbox zero" on my feeds, or whatever else) was a text post by the feed's author telling everyone to follow some new feed instead.
And other authors don't even bother with that; they use a blogging framework that generates RSS, but they're maybe not even aware that it does that for them, so instead they tell e.g. their Twitter followers, or Twitch subscribers, that they're moving to a new website, but their old website just sits there untouched forever-after, never receiving an update to point to the new site which would end up in the RSS feed my reader is subscribed to. It's nonsensical.
(And don't get me started on the fact that if you follow a Tumblr blog's RSS feed, and the blog author decides to rename their account, that not only kills the feed, but also causes all the permalinks to become invalid, rather than making them redirect... Tumblr isn't alone in this behavior, but Tumblr authors really like renaming their accounts, so you notice it a lot.)