The apt.postgresql.org crew have a package morgue for old versions at atalia.postgresql.org/morgue/ . It's not a full repo, but you can fish out needed packages manually and install them. This is a *lifesaver* when trying to examine a core file a customer system where debuginfo wasn't installed, or trying to reproduce a subtle version-specific issue.
Do you have anything like that? If not, do you have any interest in it? I'd really like to get something like it going, and rather than creating one in-house at 2ndQ where nobody else lands up benefiting, it might make sense to help out with one for the community.
What I'm thinking of is a selective rsync to an archive repo, where packages get copied but never get deleted, then createrepo_c runs in incremental mode (--update --retain-old-md-by-age=5d) to index them.
An alternative is to ditch the repo indexing and use an AWS S3 bucket to host an unindexed package slush pile, like the apt morgue. createrepo can't run sensibly on s3-hosted files. But s3 is cheap - 2c/gb/month, or less if you go for infrequent access mode.
Thoughts?
I can always set up my own mirror inhouse for 2ndQ, but I'd rather work with you.