I like to add to this that we live in a time of growing acknowledgement for web privacy (look at the wiki page Right to be forgotten) where even Google responds to. For different reasons people would like their names not to be traced back till we-don’t-know-when. It would be a very nice gesture if WordPress could discuss internally if they could make an option to make your account really invisible. For the argument of keeping posts visible for other users: simple solution would be to just display the name as @notactiveanymore.
Hopefully this can be taken into consideration!
