Am I the only one spooked by the fact that to opt out, you now need to have your passport with you? (and for _domestic travel_ no less) Given that the facial databases contain your data regardless, and the amount of in-airport surveillance (in that you're not gonna avoid being observed and logged), It's more of a, "we're gonna make you present your papers regardless, pick your poison"
The whole point of this is to implement the Congressional mandate for exit tracking without the more traditional exit controls of getting your passport checked and stamped upon exit (which most countries do).