The Glaser safety slug is already on the market for home defense.
With a 9mm load, when it hits anything, it will start to disintegrate, if it's a human body, sheetrock, etc.
from their website FAQ's:
The GLASER Safety Slug was carried by the sky marshals on planes for years, would they be safe on a commercial jetliner ... ?
The Safety Slug was extensively tested by the sky marshal service during the 70's and 80's. They were convinced that the GLASER had the most effective stopping power at close range, with the least likely hood of structural damage. Glaser is an excellent choice for any situation where there are a large number of people; where the danger of a ricochet hitting someone is great; or when a bullet passing through interior walls is a concern.
the website is here:
http://www.safetyslug.com/