I think the conflict here is that, for the "non-IDE" programmer, Rust's tooling is best-of-class (IMO). If your idea of an ideal programming environment is running vim/emacs/sublime/atom and maybe a terminal, Rust's tooling is great.
However, some programmers like an IDE more. Which is fine, but for this type of programmer, Rust still has a long way to go. There are some immature plugins for existing IDEs, and even a couple "rust-specific" IDE projects, but nothing near what (say) Java or C# have.
As a vim user I can attest to this. Rust tooling is better for me than any other language I have ever used. Only thing I ever wish for is a REPL, which is a big ask for a language like Rust.
Rusti isn't 'there yet,' unfortunately. It is forced to recompile the entire project for every line entered. Aa far as I know I also can't do things like set 'breakpoints' that will pause execution and drop me into the REPL, like Ruby's binding.pry.
This is a very hard feature for compiled languages, its just a con of this execution model (which is has a lot of pros).
I believe the playground is just a well-sandboxed Rust compiler. It doesn't have any of the fancy features of a REPL, such as allowing you to refer to the state of prior runs.
However, some programmers like an IDE more. Which is fine, but for this type of programmer, Rust still has a long way to go. There are some immature plugins for existing IDEs, and even a couple "rust-specific" IDE projects, but nothing near what (say) Java or C# have.