> What would be a good use case of Rust than Golang cannot do given its extra complexity and potentially lesser monetary reward?
Anything where low-level control is required. It's not clear if there are true-Rust web apps in the wild (as opposed to web apps with some services in Rust); as far as I read, Rust web programming is ugly.
The market still offers few positions, largely dominated by crypto. I have the impression that it will still take many years before the field will move to Rust (where appropriate).
> Any advice on which I should pick as a new language to learn?
Depends on the concrete goals. If you want to make a career, Golang is the safe bet, by a very long stretch. If you want to have fun, try both, and you'll naturally find your inclination, as they have a radically different flavor.
> Anything where low-level control is required. It's not clear if there are true-Rust web apps in the wild (as opposed to web apps with some services in Rust); as far as I read, Rust web programming is ugly.
There are. I run one. Written in pure Rust. 160k lines of Rust code in total, serving over 3 million HTTP requests per month. Best choice I've ever made.
Rust especially shines when you need to maintain a big project over a long period of time. People often say that Go is much more productive than Rust, and in most cases that is true, but as the size of your project increases and your expertise in the language increases this relationship inverts, and Rust starts to be much more productive. Pick a right tool for the job.
What Rust web libraries/frameworks do you use and recommend? How long does your Rust project take to compile?