Why use Rust for web development? There are very few web back ends in the world that need the speed of C++ or Rust.
Java, C#, Go, Haskell, OCaml are much easier to ramp people up with and hire for.
Java, C#, Go, Haskell, OCaml are much easier to ramp people up with and hire for.
And then there's the environmental cost of slower code. How many tonnes of CO2 emissions are higher level languages responsible for daily?
Sure. If it's just as easy for the task then why not?
But I wouldn't recommend Rust for web development for the same reason I wouldn't recommend C++ for web dev: complexity. Obviously, this is entirely subjective but I don't think either language will ever be easier to write than Java or C#, especially for beginners.
I used to TA a freshman data structures class. I can't imagine ever going to a class of new programmers and trying to explain to them when to use Rc<RefCell<Vec<T>>> vs. Rc<Vec<RefCell<T>>>.
I'm interested - how do you teach it? I would have thought that the type system could make these things easier to visualise rather than harder, but then I don't have teaching experience.
Idiomatic Rust makes single-threaded interior mutability very, very rare. I don't remember ever once encountering the dilemma of "Vec<RefCell<T>> vs RefCell<Vec<T>>", in my own code or elsewhere.
In fact, my current project (https://github.com/team-worm/spice) involves an HTTP server written in Rust. Like you suggest, managing state across requests was one of the harder parts (both for myself to work out fully and for a team member who started with no Rust experience to grasp).
However, much of that difficulty was intrinsic to the problem- the HTTP library we use is multithreaded, so for correctness we have to synchronize access to the state. Instead of discovering this by way of race conditions or hard-earned experience, Rust enforces it for us. Team members who have never used Rust before can be trusted to go in and work on the server without worrying about causing subtle concurrency bugs. They hit the brick wall of error messages instead.
At the moment a lot of hobbyists are doing web stuff in Rust. Commercially I think usage would be in the same vein as the common pattern of rewriting Ruby services in Go if it starts to limit performance.
If you've got a particularly hot lambda function, rewriting it in Rust is a pretty simple way to save a bunch of money.