Sorry, meant “Keyset paging would make perfect sense on a page like https://www.inaturalist.org/observations”.
Yes, but once you get to page 2 in this scenario, when happens when you click back to page 1? Do you see your 15 reviewed and 15 unreviewed observations, or do you see the 15 unreviewed and 15 more unreviewed that used to be on page 2? Or worse when you go from page 10 to page 3 after having reviewed just a few on each page in between? What you’re proposing would work just fine for a
“More” or a “Next” button as I described above, but not so great for pagination. It would work fine if we ignored whether or not you’d reviewed stuff, but that’s sort of critical to the experience.