The problem that Debian has with rust packages is that they try to apply handling a C-style dependency chain (usually only a few C libraries with large scope) for the rust crate ecosystem (a lot of dependencies with small scope). Having to maintain 732 just for one release of a new package is not sustainable.

I don't understand why the policy is not: pulling all crate sources and prepackaging into a tar with associated licenses. The source tree then is part of the package which can still be built from source and gets linked statically.