Eons ago Dan Wesson proved the efficacy of the "three piece" barrel system - a shroud, barrel, and barrel nut. Competition shooters (myself included) utilized the ability to set the BC gap close to maximize power during silhoutte competitions.
Smith does it differently, but the engineering behind it it the same. A barrel that is not tensioned into the frame doesn't need to be a thick and robust, and accuracy is enhanced because the shroud acts to "pull the barrel forward" away from the frame which sets it in TENSION. A traitionally screwed in barrel is NOT under front-to-back tension and is not and never can be as accurate as a barrel that is.
The only thing "wrong" with what S&W is doing is they have chosen to make the barrel/shroud a factory serviceable issue versus user based...I suspect they'd still make plenty of cash with a user-screwable barrel because people like to have an entire gun with a given barrel.