If I'm misunderstanding your question, please provide more details.
I use elfeed on emacs (https://github.com/skeeto/elfeed) with the time descending sort, and it does exactly what you state in the question. The newest feeds float to the top and the older ones sort to the bottom.
If I let too many build up, I simply mark them as read and they disappear from the list. They aren't deleted, and I can search for them at a later date.
In your case above on not wanting to "Mark as read", elfeed has an filter ex. @6-months-ago that when a feed reaches that age, it disappears from the list. A smaller time scale like @2-weeks-ago might be closer to what you are looking for.
Of course, all of this text is irrelevant if you aren't using the emacsOS tools and don't want to mess with setting them up. But since the RSS spec was invented, I've not worked with any of the readers that fit my personal approach as well as elfeed.
Good luck.
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.
This already exists. It's called RSS.
https://lukesmith.xyz/blog/a-guide-to-using-rss-to-replace-s...
The only major issue with RSS is a dearth of decent feed-reader software. I personally use newsboat[0], but elfeed[1] also looks pretty good if you're an Emacs Chad.
[0] https://newsboat.org/ [1] https://github.com/skeeto/elfeed
For podcasts (since these are also technically feeds) I use AntennaPod[3] on my Android phone, but don't use it too often because of all the time commitment required with podcasts.
[1]: https://tt-rss.org/ [2]: https://github.com/skeeto/elfeed [3]: https://antennapod.org/
Since I am using Emacs, elfeed (https://github.com/skeeto/elfeed) is my best choice for RSS reader.
And very important I use HN feed filtered by number of points (thanks to hnrss.org): https://hnrss.org/newest?points=500
[1]: https://github.com/skeeto/elfeed [2]: http://spacemacs.org
There's also Elfeed for Emacs https://github.com/skeeto/elfeed
There's also newsticker.el but I never could get it to work.