"i'm going offline but i want to hear about X, Y and Z when i get back" is a level of interaction with a messaging system that i personally find hard to imagine.

With Quassel at least, private messages show up elsewhere, tagged messages will generally be color-coded for easy identification. I suppose that people who participate in busier messaging systems than #ardour on libera.chat may need the sort of thing you're referring to, but it is so foreign to me that it's beyond my imagination.