While much progress has been made on studying notions such as Knightian uncertainty, sentiment, confidence or sunspots, more work is probably needed before they can be part of our standard modelling toolbox. A challenge is of course to come up with tested and robust behavioural theories.
Another important departure from rationality that is of key practical concern is how simple behavioural rules adopted by market participants in normal times can lead to entirely different outcomes or even to market meltdowns in crisis periods.