Sure for Bing type interfaces it makes sense but if you consider what it is more holistically there are two questions: 1) do you want it to be non-deterministic

Sure for Bing type interfaces it makes sense but if you consider what it is more holistically there are two questions: 1) do you want it to be non-deterministic and hope the first answer is the one you want everyone to see and 2) do you invalidate the entire cache every time there's a minor update to the model? How else do you tell which keys to remove? You'd basically be removing the entire cache every release