This is the approach we’re currently working on in WIP: A11Y improve heading-to-heading nav, fix infinite scrolling by awesomerobot · Pull Request #34589 · discourse/discourse · GitHub
As you suggested, we’re adding some light screenreader-only headings on all posts (cloaked or not) as well as a heading that will trigger more posts loading, along with the announcement that loading is complete.
It’s still a work-in-progress, so it will still need some refinement, but hopefully we can get this fix available for everyone soon.