It's technically possible to look up Namecoin name registrations made with the same key as memo profile, and display the unique name if a match is found
They will still get a notification if you reply directly to them, but should they encounter your posts anywhere else, the posts will be hidden, showing: "X has been muted"
Just added this. Now muted users are hidden for good, even in notifications. (If you recognise your address, no worries I've unmuted you, just testing)
That is easily solvable on a UI side as well. Highlight all those imposters tricks with color. Works pretty well, especially when combined with "connections" percentage.