Pulling the data when a user requests a post/comment (with a cooldown/cache for popular posts) isn’t any more or less scalable
That would definitely be less scalable. That would entail pulling every single time a user views a post or comment. That’s simply not feasible. There are far, far more views of content than there are posts, comments and votes.
Also what about stuff that isn’t seen? What if nobody is logged in or nobody looks at the New sort? You need the votes before you even show the user anything, otherwise you can’t sort the votes.
But if it has to be a push model, why doesn’t feddit.dk push the votes it knows about along with the rest of the data?