What we need to revive RSS is have a true integration into browsers. Your bookmarks would display the numbers of unread posts and there is probably more great stuff to do.
Honestly just returning the icon that appeared when the site had a feed would be a huge win. Browser integrated feed-readers and bookmark notifications were nice but dedicated RSS readers are probably going to be better. You can click the feed icon and the browser can redirect you to your preferred feed reader.
There are extensions that do this but having it built-in would make it widely available and easier to set up.
https://support.mozilla.org/en-US/kb/live-bookmarks