I think if an MRI was ever used for airport security screening it would cause more damage and disruption than the terrorist bombs it purports to detect.
The idea behind the recent boom in low-field stuff is that you'd like to have small/cheap machines that can be everywhere and produce good-enough images through smarts (algorithms, design) rather than brute force.
The attitude on the research side is essentially "por qué no los dos?" Crank up the field strength AND use better algorithms, in the hopes of expanding what you can study.