Looks like incremental compilation hit beta in Feb: https://internals.rust-lang.org/t/incremental-compilation-be...
For me it's just fine that cargo doesn't support every odd use case of of the box in exchange for supporting the majority of use cases with virtually no effort. CMake hardly supports anything without a bunch of scripting--this includes reproducible builds, unit testing, etc.
That, alongside the lack of incremental compiler and linking, means my C++ work projects (native libraries for Java and .NET) actually do compile much faster than Rust occasional weekend projects.