Understood. I think this will get more clear over time. Right now we're stabilizing things we clearly need, deprecating/moving out things we clearly don't want (for now), and leaving the rest unstable.
In the long run, unstable items should be on a "path to stable" or else be removed. I think after the dust settles for 1.0 we'll re-evaluate the remaining unstable items under this metric.
Yep -- good eye! These were also specifically not stabilized because they seem somewhat niche.
FWIW, these features could probably be moved out of tree before 1.0, it just hasn't been a core priority. If you wanted to put together an RFC/PR, I'd be glad to review. (It might be worth putting together a more comprehensive list of such APIs that we could reach consensus on beforehand.)