Earlier quoted context omitted.
0-install ( http://0install.net/ ) or even better - Nix packaging system ( http://nixos.org/nix/ - they claim to be a purely functional package manager)
Damn straight! I don't understand why so few people know about Nix. I'm hoping Nix(OS) will take off eventually. I try to play with it from time to time, but I haven't made the investment yet to really contribute.
come to think of it, there is nothing in aptitude that prevents this kind of an approach (including the unique hash paths). It will get you to 75% of Nix functionality, which IMHO is good enough.
I dont think Redhat.or Ubuntu will want to do that though. Their business model revolves around the walles garden.