Thanks, glad the post helped.
It's been my experience feature requests through the AWS forum aren't effective. I've seen a lot of requests get acknowledged but nothing happens for years, if ever.
From what I can tell, AWS prioritizes feature requests from paying customers telling AWS what they want through their account reps.
Rusoto sends a user-agent header on all requests to AWS, with versions of Rust, Rusoto and OS details. This change was requested and implemented by an AWS employee so they could gather metrics on Rusoto's usage. With this data in hand they can see how much use Rusoto is getting, to see how much interest there is. See https://github.com/rusoto/rusoto/issues/379 for more info. 
I see three avenues to making Rust officially supported on AWS:
- using Rusoto to bump those usage metrics from user-agent information
- use Rust on AWS and be vocal about it via tweets, blog posts, etc...
- tell AWS account representatives you'd like to see Rust supported for your use case: faster and safer Lambdas, easier deployment of Rust apps on Elastic Beanstalk, etc...