I prototyped and wrote a blog post about that too: http://williamedwardscoder.tumblr.com/post/15581427232/self-... ;)
There was a voting graph in the background. Nodes are users and edges between users are weighted by the total number of mutual upvotes they had over all stories. With this graph you could give more weight to a story to a particular user if "similar" users had upvoted it, and everyone sees a unique front page.
One of the hard parts was how to sort stories based on these new weighted links. HN never reveals how they sort, though there is some historical evidence when things were simpler. However I found if the sorting was linearly proportional to votes, and a power law in time, then it didn't matter so much what the particulars were, and you could still reorder posts in an HNy way.
If anyone wants to talk more about this I'd be happy to revisit this project! :-) Contact info is in my profile.
The lack of such a "filter bubble" is why I actually treasure HN more than other similar news aggregation sites; it exposes me to ideas, sites, and viewpoints outside of those I'm normally interested in, whether I agree with them or not. :)
(My prototype split above the fold into "unfiltered unrated" stories and the filtered stories, so everyone was always exposed to some irrelevancies.)