[necovek]

How fast would it be to get a delta between any two of the 2,000 builds in a single elfshaker pack?

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.

[peterwaller-arm]

Yes you could do that. On the other hand, all revisions for a month is 100MiB, and all revisions we've built spanning 2019-now are a total of 2.8GiB, so we opted to forego implementing any object negotiation and just say 'you have to download the 100MiB for the month to access it'. I think you could a push/pull protocol could be implemented, but at that point probably git might do a reasonable job in that case :)