Isn't the same link being posted over and over already such a filter?

Maybe of some kind, but not the same.

I'm reluctant to introduce mechanical postings for anything because it's important for the content here to have variety and not be predictable. And also to be related to the people in the community.

And thank you for this. Despite my gripes with it, HN is indeed a community,not a 'platform'. Thinks like this policy keep it this way