@giemme Sorry, that's not quite what I meant. It doesn't matter if you can define custom categories or if they're preset. What I mean is, relationships between humans are more organic. To use the example in your mock-up graphic to make the point: I work with friends, and sometimes do other categorical things with those same people. If one sends me a message, there is no way for the phone to know if it's work related, friend related, or sport related, or perhaps something else entirely. So trying to group notifications into such categories will fail.
So it will always feel weird to try and split relationships categorically as such, when they are so organic. It seems like you're trying to solve a very specific problem that you might be having, but I don't think it scales well to general usage.