I get that it's out of scope right now, but it'd be so cool to have a decentralized solution for regional caching
Unlike most other packaging systems though, Nix packages are rebuilt when there's changes to any of their dependencies. This results in a huge amount of storage data used in their caches compared to other systems. Not to mention the compute power required to rebuild those packages.
For example, let's say something like `glibc` updated with a new patch. Every single package that has `glibc` as a dependency needs to be rebuilt, along with every package that has any of those packages as a dependency. This could easily cause the rebuild of tens of thousands of packages, even if they are only dynamically linking to it.
IMHO I'd prefer to see compile-time caches like ccache or sccache be better integrated into Nix while still providing the guarantees that a functional build system provides. That alone would save massive amounts of compute power when rebuilding packages, as you'd essentially only need to recompile the files that change in a package. Not only on continuous build systems like Nix's Hydra, but also when just rebuilding packages locally. This won't solve the storage cost issue, but would definitely alleviate compute costs.
The preferred way to do this is to override `stdenv` with `ccacheStdenv` on the individual packages that would actually benefit from the compile-time caching. Such as for large packages that you already have overrides for, or for nightly packages that get updated extremely frequently and don't have the chance to be cached upstream (such as firefox-nightly). The NixOS Wiki has a pretty good article on this: https://nixos.wiki/wiki/CCache
I personally use this for any packages I override in an overlay to reduce build times significantly.
While we're talking about opensuse, perhaps there's a way for them to exist on the opensuse build system?