I would add to this that tag URIs (see RFC 4151) are a fantastic way to mint entry IDs.

Yes, use Atom 1.0 <3

As the author of an RSS reader, I would agree with most of that article, except the HTML / Styling section. It is full of misleading information.

1. You can use CSS, but expect that most readers will completely ignore it. Even widespread ones, like Feedly. Those that do support it will offer a small subset, like text styles, but don't expect positioning or flex-layouts to work. If you want to try the capabilities your reader, this is a test feed: https://test-rss.downread.com/styles.rss.xml

2. Don't just prefer inline CSS, use it, because any sane RSS reader will filter <style>.

3. Yes, semantic elements will generally work. And not only those listed, but also things like <table>, <figure>, and sometimes <aside>.

4. Agree about JavaScript. Don't use it.

5. Decent readers will support <video> and <audio>. But <iframes> are even better, as long as you use common providers, especially YouTube. X, Instagram and Facebook are also relatively widely supported.

6. Agree about forms. At best, they will be used as rendering hints, but forms won't work.