Well, back in the day firefox had a rss reader integrated and would detect feeds and put a nice rss icon in the location bar. That kind of addressed the first two points.
As for discovery, I think much like Twitter and other social media, the best discovery is one person you follow just plainly links to some other.
For me RSS reader in Firefox was the best idea hands down because of its simplicity and how well it was integrated with the browser: you'd click on that icon in the address bar and page with summary (originally you'd add feed directly to the bookmarks) and subscribe button would appear and then, modal asking where to put new channel/live bookmarks folder. With bookmarks bar on, you could have a handy folder or folders that changed list of "bookmarks" all day and you could glance thru headlines without actually opening a page. And IIRC, the default RSS channel was customized among all language versions - for British English it was BBC News. I really liked this feature and Mozilla removing it angered me much. For a while I tried using something else - RSSOwl or Feedly, or Nextgen Reader for Windows 10 but nothing could replace it for me.
Somehow Mozilla deducted that this feature is no longer needed due to the maintenance, performance and security costs [1] and it will be removed in v64 which was of course done. This reader was known and luckily at that time already ported as an extension to Chromium-based browsers as e.g. Foxish [2], which then was bring back as Firefox extension Livemarks [3]. That's a long way around trip.
Indeed, it's pretty easy to 'retweet' something from another feed. RSS items can have a <source> element in them, just point this to the original feed. Et voila, you're 'retweeting' with RSS.
* how to make it easier for users to start using feed readers
* how to make it easier to subscribe to feeds
* how to help users discover new content