This really is a great thread and I love the mental exercise. ^

The Terry doctrine has never been tested with a non-LEO, as the basic test is whether or not one's freedom of movement has been impaired in a significant way, up to and including an arrest (at which time a search incidental to arrest is permissible). TSO's are agents of the government, but lack powers of arrest, and cannot be considered law enforcement officers.

A Terry Stop is not based on a "reasonableness" test, but a balancing test, where the rights of an individual to move about are weighed against the government's right to determine if something criminal is afoot.

The consent that applies at a checkpoint is implied; by presenting yourself you are implying that you consent to a search of your person and property. TSA conducts an administrative search, which is an exception to the search warrant requirement. The inability to withdraw an implied consent also occurs with DUI cases - refusal to comply with a breath or blood test results in separate charges, so in reality you either comply or get arrested.

All of this will (and should) result in a test case somewhere. I believe a lot of weight will be given to a traveller's assertion that a certain "intimidation" factor is present at a checkpoint, and TSO's, to a great many people, are LEO's.