what masto actually needs and craves is diaspora's aspects
sometimes i don't want my fuckin besties to see something (think AD accounts) and sometimes i only want to say something to folks i know live around me etc.
you don't even need a alt when there's aspects
here's the user guide on aspects:
every machine has an ethos. the idea behind aspects is when you decide to start sharing your stream with someone, you don't have to share the entirety of yourself. there's never an all or nothing. so, from a single account you might want to share some things with certain groups of people but not other things. making a new aspect doesn't require that you have a new account to share out and do the same old work of getting everyone you'd like to see it to follow your alt again – you can just make the aspect and publish to it.
what we've got here instead is concentric circles: the entire gnusocial network, your followers, any single follower. so, outside of dm (which, like all the privacy here, was compromised even before the exploit), anything you publish on your timeline will at the very least get to every single person who follows you. following people and accepting followers then becomes an all or nothing affair. that's not good consent practice but it is pretty much status quo for social media. we can do better than status quo.