With all respect to RSS, Endless allows for users to interact with posts. Which means you can upvote and leave comments for posts on websites that initially do not implement a way to do this. Thus, you don't have to create an account for that. Besides, with custom extractors you can see posts from pages with no RSS support. Also you will be able to see trending and controversial posts based on upvotes and comments on your front page in the upcoming versions.
The votes and comments are local to the Endless instance, not forwarded or federated anywhere, correct? So for example if I run a personal one I'd only ever see my own voting history?
it could be very interesting if there is a sidebar of content engagement this way? perversely also useful if Endless has a lot of engagement as a monopoly
I'm not the author, but my guess would be that some of the suppoorted websites do not offer an RSS/atom feed to be leveraged by an RSS reader app. So, at a glance, it seems this app aggregates content for those sites/app which lack rss feeds...as well as includes sites which might already have rss feeds. At least, i think.