I am pretty happy with the current state of things, except that it would be really great if debugging Rust code using Visual Studio's debugger worked approximately as well as debugging C code using that debugger does.
In Visual Studio, and probably other IDEs, it is relatively easy to create custom build rules for building Rust projects using Cargo, and it's really just a minor and infrequent inconvenience.
I think this might be true, but I think there are language features that are blocking progress on many other library and language features: const fn and intuitive support for array references. I feel there have been lots of discussions and proposals about things that were ultimately concluded "we'll just wait for const fn to solve that" but const fn seems to be getting further away rather than closer. Similarly, improvements to array reference support—e.g. slicing a [T; N] into a [T; N - 1] for some constant N > 0—seems to be blocked on the "generics parameterized by integers" feature. I think implementing these features are likely to have at least as big of an impact as implementing impl Trait return types.