The chrome extension Calibrate apparently used to do this, but it doesn't seem to work anymore. The feature seems like it'd just help the accuracy of prediction markets in general, because aggregating independent impressions should theoretically be a better way to distill independent sources of information. So it makes sense to have as an integrated feature.

This is in line with the idea that you should "blurt your priors" so you can notice what you even believed before you update on new evidence. Otherwise we're prone to think that our new prediction is what we believed all along.