According to plans the new package format and app installer would be complementary to apt/dpkg and would not be replacing the existing traditional Debian packages. The new system has been conceptualized as a system that will sit on top of the existing base system. Colin Watson has detailed the plans regarding the new package / app installer on Ubuntu-Devel list.
Some of the features of the system are that the applications wouldn’t have any dependencies in between them but the base system; everything needed by an application would be bundled in a package and then shipped; each of the packages will go in its own directory; the package format / build will be more or less around Python and JSON; and the entire package format would be purely declarative.
The code has currently reached proof of concept stage, written in Python, which is working with the current system as intended. The code will be released sometime next week.