Appear offline to specific users

Problem

If my memory isn't tricking me a long time ago I saw a screenshot from a really old internet messenger that had a option to appear offline to specific user(s). I think that would be cool to have on Fluxer. I don't know if this can be integrated with federation though :(

Proposal

When right clicking a user there would be a option to appear offline/invisible to them. This would be global within groups chats and mutual communities