What I'd like to see is sites like HN using tools like this. So that rather than see some kind of popular consensus about what makes a "good" posting, I see (or have the option of seeing) the kind of thing that I want to see.
About "wouldn't be that difficult": no, not given a good and appropriate recommendation engine. However, is there one? For example, in context, we're talking about DirectedEdge. It seems to be aimed primarily at product recommendations, not link recommendations. And I'm not sure these are really even the same problem.
According to my reading of the documentation I think the recommendation engine operates on the data set that you specify regardless of the content. It operates on link graphs and group recommendations not the data itself. Basically, the data that is represented is invariant. The operations it does is like a group based recommendation service.
EDIT: And if done right, it could render questions like this one irrelevant: http://news.ycombinator.com/item?id=1035206