Good ideas and conversation. No ads, no tracking. Login or Take a Tour!
After reading everyone's comments, feedback, and use cases, I don't think you need to change a thing. My reasoning behind username/content permanence was that people should be held responsible for what they say and do online, just as they would be in the real world. A "staged exit" like you propose would not dissuade the trolls from trolling, because they can still disclaim responsibility for their actions. It would only make a more complex system, with minimal practical utility.