It's worth noting that Void Linux (and maybe others) does indeed keep all its (largely declarative) package recipes and build tooling in a single git monorepo,

It's worth noting that Void Linux (and maybe others) does indeed keep all its (largely declarative) package recipes and build tooling in a single git monorepo, although it does not keep copies of the upstream source because (package, version, url, checksum) is assumed to be idempotent, and some of the stated advantages are real: >Simpler collaboration: every package uses the same process, and the same tools, and it’ll be easier than ever to help with other people’s packages. >Enables distribution-wide changes in general: With all the source code for everything in one tree, in on repository, it’s feasible to make changes to Debian that affect many packages. For example, back in the day Debian took seven years to migrate /usr/doc to /usr/share/doc, and that can now be done in one commit.