I doubt this is by any means the most important performance issue that Debian package installation faces. It looks like the speedup discussed here is in the no-update case, which is nice, but not the only case. I stopped using Debian at home several years ago, and one of the main reasons was the incredible slowness of groping around in GNOME's moronic XML settings database during every update. Upgrading schemas and whatnot. I still use Debian at work and I note that it is still prone to building and rebuilding initrd during an update when it should only be built once. On a recent update initrd was built for the kernel that was being _uninstalled_ which was awesome.