Jonas' suggestion is interesting, even though it is by no means new. In any lengthy discussion about software installation, someone will suggest union mounted disk images. I am wondering what the implications are concerning system overhead; extracting the images to memory on startup, having dozens of mounts, handling path conflicts between packages. Possibly an even larger challenge is dealing with file system queries; files from the disk images must appear in the BFS attribute indexes - how is this going to work? Regardless of the chosen package format and handling, it's important that any package should be installable both system wide and in a user's home directory. This means that file paths must be relative and work equally well in /boot/common and /boot/home/Joe/config.