If you're an Emacs user, I'd really recommend checking out elfeed (https://github.com/skeeto/elfeed). You can subscribe to RSS feeds just by adding a line to an org-mode file, and then organize and tag all your feeds with all the usual org-mode features.

Also, I think the author is being a little pessimistic about the state of RSS. It might not really be "mainstream", but almost every blog I visit has a feed, also Substack offers feeds, YouTube channels, Reddit, etc. I only just started writing my own self-hosted blog, and within a week or so I got an email asking me if I have an RSS feed. RSS is very much alive and well, if niche.