Here is one post about writing an Aho-Corasick implementation in Haskell which is as fast as the fastest Rust implementation: https://tech.channable.com/posts/2019-03-13-how-we-made-hask...
While itβs true that Rust shows promise in security and embedded, some of the early adopters have been in the server side and microservices.
You could call Java is niche for the same reason. Some of us want to write native, low overhead code in a language that has a sane design (only disparaging C++ here). It's about time C++ had more alternatives.
Anything on the internet should be cautious of memory unsafety issues. Something like an image processing library I won't consider 'security focused' yet I would trust one written in Rust over one written in C.
I think Swift is where .NET was in its first decade. While capable of so much more, it is limited by its designers and primary purpose so it cannot go beyond. The tight coupling to UI products is a burden an ecosystem carries. Java won in the backend not with is UI, JavaScript with node/npm before Angular reset the frontend and C# just when .NET Core pushed it into spaces it has not been before (apis, lambdas, etc).
Swift has many nice similarities with Rust and other current languages from a pure syntactical/language perspective, while aiming to be a GP language. It definitely serves a broader audience than Go, whose main target is server programming. Swift's main target is Apple UI programming, however, the language is capable of so much more.
Which is why Open Source is good news. It may make it escape its Apple box.