Sounds like a challenge :) First, this doesn't have to be for each pageview. Crudely, you want every story to have a vector in some giant hyperspace characteri

Sounds like a challenge :) First, this doesn't have to be for each pageview. Crudely, you want every story to have a vector in some giant hyperspace characterizing it, and every user to have a vector precomputed offline based on their previously shown affinities, and take dot products. This is not necessarily easy, or computationally very cheap, but the payoff can be pretty big. I believe LinkedIn runs something similar to this every night.