I've been slowly iterating toward building "safe" abstractions around the Erlang NIF interface in Rust, because a broken NIF can bring down the entire BEAM VM, and I very, very much want to have the kinds of compile-time safety checks that Rust provides me when writing NIF modules for Erlang software.

For me it's become, "Anywhere I would use or have to directly interface with C; evaluate using Rust instead."