Breasts, being semi-fluid, are going to be problematic as long as they are not simulated in a physics engine of some sort, like dynamic hair and clothing.  To do it properly, the breasts would have to be dynamic, a ribcage structure would have to be defined, and they would have to be able to be contained and re-shaped by clothing as well as gravity.

Until then, morphs and/or magnets are pretty much our best option.

In my uneducated newbie opinion.