Nice. Idea: it would be cool if HN kept the original submission just as signpost or tombstone, that would be incredibly transparent (otherwise tracing URL modifications depends entirely on the submitter mentioning it and being honest about it). Although I admit this is a very minor feature. I know stack overflow does a vaguely similar thing with duplicate posts, where they'll usually be downvoted and closed quickly, but they often remain as 'signposts' linking to the preferred post on that topic.

Btw, thanks for all the work you do.