Interesting. I wonder if this can also be [ab]used to, say, deliver deltas of programs, so that you can have faster updates, but maybe it doesn't make sense.
If that's reasonably fast, perhaps an approach like that could work: server stores the entire pack, but upon user request extracts a delta between user's version and target binary.
Still, the devil is in the details of building all revisions of all software a single distribution has.