'Already there' in that case is just 'there's a package for Rust and cargo' (but not necessarily RusTLS). That still leaves a significant integration challenge.
Which challenges are not showing up there ? There are packages, and they are usable to build other packages.
2) "My distro does not include a RusTLS package. How do I package this? Do I have to add Rust to my build dependencies now? How do I add the Rust steps to my build system? Where was that CMake manual again..."
Rust has a bright future ahead, but yet another TLS library doesn't justify the overhead and complexity of bringing Rust into a build of non-Rust code. Now, if most distros were to offer a rustls package, this could be entirely different story.