Privacy in conversations:
Have supported private groups and circles/aspects for years now. I don't know how anybody would think that privacy is optional. I don't see a lot of people taking showers in the public square. If you're interested, I've made this work available to other ActivityPub services that wish to implement it through a delivery model I call "conversation containers". It basically extends on some existing FEPs to let you implement contained conversations and not have the protected conversations boosted across the fediverse. I've got some background docs if you're interested.