We make decisions on a case by case basis and people can judge for themselves if they think it is reasonable. Clearly defining where you stand is very hard, and we don't think we'll do a good job at it. Giving a definition and then backtracking won't win us any fans either. Anyway, it will be more PG-13 than the old Reddit.
We'll never delete data, we will make the repositories private. You will have to move your public project elsewhere. For significant projects we're open to making it public when you've replaced the repo with one announcing the new location.
