The first response is on the right track.
A D frame sized revolver (small frame .38/.357 Six Shooter) would make more sense than a new Model 12. I have always felt that the Model 12 (post 1973) was a consolation prize, due to the unfortunate fate of the C frame. A Model 12 might be light, but it is still dimensionally a medium frame revolver.
With Kimber, Colt, Taurus, and Charter offering small frame six shooters, it would be nice to see S&W offer a quality competitor. Some might be concerned about internal competition with the J frame. Honestly, I think there is room for both. The J frame makes for a better pocket revolver and a D frame sized gun makes for a svelte belt gun, that is more comfortable to shoot with .38 + P ammo, and easier to carry than a medium frame revolver.
If S&W can produce ridiculous niche items, like the Governor, they can give the Model 73 concept another try. With that said, a new 3" 38 +P Model 12, along with three inch 64s and 619s, would be very nice medium frame offerings.