I think PMU should have the ability to block players, in a way that they cannot see or interact with you or you chat messages, and you cannot see their messages, see them, or interact with them. I define interact as entering your house, being affected by their moves and thrown items, and seeing whether they are online or not. They would still be shown in guild lists, be shown in the total player count, and items they drop will still be shown.
This feature is not meant as a replacement for bans or to be used just for ban worthy behavior. This is only meant to stop players from having to put up with players whose behavior is bothersome to an individual.