I'd love to be able to set name/avatar per topic I'm posting to. Bit like having many aspects to your presence - when I'm talking about gunpla, I use this name+icon, but when I talk about security - a different one. Ideally with enough settings to make it impossible to tie aspects across to a single human.
This is my major problem with Reddit - it's right now the place for obscure topical communities, but I'd prefer my "water jet enthusiast" persona be separated from "shitposts about cycling in Dublin, Ohio" persona. On Reddit, this means separate accounts, which is bit cumbersome to manage.