The big problem that I took away from the availability report was the one where they lost acknowledged writes. They might not need the scaling, but they do need the ability to lose the leader without losing writes. (It would be preferable to reject the writes and become unavailable rather than to acknowledge writes only to discard them minutes later. No external API user can handle the case where "Github acknowledged my writes, and I read them back, but now they're gone". But they can handle "Github returned 'service unavailable' when I made a write".)