I personally am most excited about Rust's future with WebAssembly. Wasm is the assembly language of the web. JavaScript is the application language of the web. Rust should be the systems lang of the web. Systems languages succeed because they’re the native language of the platform. For the web platform, that language should be Rust. If you need to do a systems-level task on the web, Rust should be the default choice the same way C is the default choice for systems today.
We have a ways to go to accomplish that goal, and it's going to take a lot of work, but it's one of the areas I'm most excited about for the future.
Your question is about how we get there. On the Rust side, the biggest thing is making it easy to compile to wasm. We're not that difficult, but getting emscripten set up is kind of a pain. I want to make targeting wasm as easy as targeting musl libc; that is
$ rustup target add wasm
$ cargo run --target=wasm
Or whatever the triple ends up being.
The second biggest thing is on the wasm side: right now, wasm can't access the DOM directly, but must "FFI" through JavaScript. It has a pretty huge performance penalty. It's also a similar story with threads.
Community-wise, testing against wasm in CI would be great. Given the aforementioned setup difficulties, I don't think we're ready for that as an ask yet, though.