Kyllo involved a person’s home. IIRC, the opinion of the court, including Scalia, is that out in the public, one cannot have a similar “expectation of privacy.” Hence, sniffing dogs at a public roadblock are acceptable. I would think that these airport searches are acceptable under the same regime.
I disagree, generally automobiles are provided a significantly lower degree of constitutional protection than individuals. Thus, police can search a car when they have reasonable suspicion. In contrast, a Terry frisk, which seems to be the lowest threshold for invasion of individual privacy, requires more specific suspicion (of a weapon), as limited to searching for a weapon.
The TSA searches are more invasive than Terry and are based on a lower degree of suspicion, namely none. It is hard to imagine the TSA searches being upheld without drastically altering the landscape of the 4th amendment or without creating a new exception.