It would be technically trivial for a forum built with the typical MVC architecture with data backed up in a relational database - just change some templates, point the user ID to a global 'deleted' user, and done, or something like that.

But Hacker News is a project site built in a custom Lisp variant that runs on one core, mostly in RAM from what I understand, with all of the data in flat files, and I don't even know if they have a development server. Obviously, they can do it, but it may not be that trivial.

Or maybe they could bang it out in an hour, I don't know. It would be nice if they put up a devlog and talked about some of the issues they have with updating the site and what their future plans with it were. Maybe talk up Arc and Lisp development a little.