The page content's hash or any other blueprint (an arbitrary regex match) could be checked against for resubmissions. For convenience, if resubmission should be detected, the original post could be topped on the frontpage nevertheless, because old material may as well be worth revisiting for several reasons -- I for one had missed this article before, and enjoyed it reading greatly now.
Most resubmissions are submitted by people other than their authors, who are typically not in a position to change any bytes of the content.
In the present case, speaking as the last person to submit this one (more than two years ago), I don't see that there's any harm in it at all. If this is still interesting two years since it was last discussed on HN -- which clearly it is -- then good for the submitter, who has provided the HN audience with something interesting to read.