As far as I know, and according to Wikipedia, most commercial airliners already use turbofans [1], which are high-bypass turbojets [2]. Unless you were referring to turboprops?
Almost nobody uses turbojets anymore. Certainly not airliners. Even fighter jets use turbofans.
And here's the attendant public policy: Tax the turbojects' users enough to offset the negative ecological externalities incurred by their use. That will likely make commercial SST unprofitable.