I think the "random", "changing" and "unpredictable" parts are suppose to keep the flying public confused and off-balance, not the 'terrorists'. I dont like to give evil-doers credit for anything, but I doubt the TSA and its procedures worry them much.

Maybe they got tired of FTers complaining about shoe sole height and this is their way of shutting down the complaint mill (in the name of security).

They sure reacted and changed things when it got out that online boarding passes with SSSS were undergoing the liquid paper treatment.