So there are some interesting things that #Mastodon and #Pleroma can't do. For example, Pleroma shows replies to threads you are not in (and you cannot turn this off outside the Pleroma web UI) and Mastodon cannot mute conversations like Pleroma can.

I've found this https://github.com/hometown-fork/hometown which has some interesting features, most importantly, local only (unfederated) posting, which is great for communities. I think I will run a server eventually.