Another idea is crate-build caching so local and CI can pull down a pre-built dependency, rather than building locally. This would need to handle rust versions, feature flags, architectures, compiler settings, etc. This would most help CI since the result would get cached locally

The last idea I'm aware of in this area is watt (https://github.com/dtolnay/watt). If the design and implementation was finished to allow proc-macros (and maybe `build.rs` scripts) to opt-in to a sandboxed wasm environment, we could have a local and networked binary cache for these which would dramatically improve Rust build times (and security). Some people outright avoid proc-macros because of the build-time impact.

A better alternative than distributed compilation is artifact caching. Effectively, instead of shipping .rs files all over the place to compile them, just ship .o files around. Rust already has a decently canonical solution for this in the form of sccache, which was developed by Mozilla for caching the builds of Firefox using Amazon S3 as the storage (hence the name--S3 ccache [compiler cache]).

However this might not really work well at all unless the network connection is insanely fast as the build sizes are huge with rust (especially in debug modes).