Yay! Prim breast maker Icon Allen has come out with version nine of her prim breasts, which are indeed made with mesh.
She reports that they are much smoother and that texture positioning and matching works better. (Making the texture match with the top visible on the torso is very important for verisimilitude, so that is good news indeed.)
In addition, the scripting that controls them is much more efficient--not a visible improvement, but very important; greater efficiency means less of a burden on the sim.
I have no photos to share, alas. I hope to see them soon.