I want a packaging system that relies on the features of a transactional filesystem. OK, I want a transactional filesystem too. ;-) This would make it possible to install packages without fear of fucking things up too badly on a running system, as I could just roll the back the transaction implied by the install. I can dream, anwyay.
Also, I think current Linux packaging systems like RPM and dpkg are too centered around the "one instance of this piece of software installed in a canonical location" theme. This is really nice for lots of "singleton" things that you don't really want to think too hard about (for instance, bash), but it kind of sucks if you want to install more than one instance of a piece of software on a machine or want to install as a nonroot user. Granted, it's possible to create "retargetable" RPMs and spell explicit installation locations in different ways, but most dpkg and RPM packages aren't created in ways that allow you to do this easily. I also don't want to need to install packages as the root user just to maintain the shared package metadata database... I'd rather install as a "normal" user and have per-user metadata databases that allowed me to choose the files on which the packages' dependencies relied interactively. I'll stop now, because if I don't, I'll have to do something about it. ;-)