Remembering the last thing you already been shown and not presenting it anymore is what computers used to do, back in the 1970s.
(a third advantage to RSS: because local storage is dirt cheap, it's searchable — even the stuff I'd mark-all-as-read'ed)
(when I made hotkeys to view alphabetical splits, so if I don't read for a while i still don't get presented with more than a screenful of titles at once, thanks to newsboat(1) keeping its state in SQLite, I was able to base my counts off having queried the database of everything I'd already RSS'ed, interacted with or not)
For context, I'm thinking very generally here rather than about specific use cases, but it seems to me that anything happening 'automatically' in this area can be problematic. I'm not sure what the best setup is, but I think any system that shows a list of time-sensitive stuff (email, rss feeds) should at least be keeping a record of 'times shown', 'times opened', etc.
I've got my hotkeys configured so I get a screenful of titles, pick 0-2 that look like they might be of interest, then mark-all-as-read to get a new screenful. Every now and then I get a little quick with the "Ay", and then either search, or if it was immediate markers' remorse, "l" to show read as well as unread, and pick up whatever I was FOMO'ing so hard on — often to be reminded to trust my initial judgement.
In the unlikely* event that doesn't work, well, feeds are entertainment anyway: if an idea is really important it'll come around again, maybe from the same source, maybe a different one.
* as I've said, the db elephants everything, so it's difficult to lose anything; currently it's using like 1/1000th of my disk space and I'm not sure it gets bigger much faster than storage gets cheaper.
Lagniappe: http://www-formal.stanford.edu/jmc/elephant/elephant.html