Rolling a desperate test in Blades isn't RP so isn't really relevant. Pendragon is an interesting example, i's a much more complex model of behaviour though. If love to see it in action.

It may not be RP in those few seconds you pick up and roll the dice but it is an incentive for the RP to go in particular direction. It's the game saying "if you push this situation for your characters you will be rewarded". The RP is guided to that point by the mechanism and that leads to more RP