Interesting thought. We ran into the same issue working on a recommendation system engine as well and previously tried to build a solution around it. Curious to know what’s driving your interest in post-analysis?
One good strategy that correlated with session length for us was asking questions that were neither too difficult or easy, based on what we knew of the user's level at that instant. The post hoc analysis was really meant to dig into multiple user sessions and see if the current method was working and evaluate counterfactual strategies.
I imagine the Uptrain product could help us segment user cohorts, find out which ones aren't performing super well etc. Would love to hear what you ended up building too?