That's a good idea, but it's going to require a bit of thought to implement. It might make sense to have an "advanced examples" external page for every section in the tutorial, which would sort of transform the current tutorial into an annotated table of contents. Which could be really neat! But perhaps it should wait until Rust has some analogue to play.golang.org available.
Then again I also understand that because the language changes and evolves, maintaining more code in the docs means more effort. However, this is one of the few things I've felt bugging me as an end-user. Of course I believe this can be expected to change for the better in the future as the language matures and stabilizes, but I figured I'd voice this out given this perfect opportunity. :)