The Rust SDK is built on top of the smithy-rs code generator. On the service coverage front, you'll find nearly 100% parity—There are some legacy APIs that aren't supported. It also doesn't have many "high level libraries" (e.g. S3 transfer manager) that can find for other languages.
New services will come out the same day as all other SDKs–All SDKs utilize the same automated system to deploy new releases.
The only exception is services which require extensive custom code. We're still catching up on those for the Rust SDK.