I think Zig will reserve a few interesting surprises also in the webdev world, it just needs a bit more time to get there.
I'm a fan of Rust for things like a missile control system or a stock exchange, but not, say, writing a CRM. I'd gladly write a CRM in Zig however, given the proper library support and tooling. Why? productivity. In my experience it just takes 2-3x longer to get the same thing done in Rust vs. something like Zig/Crystal/Go and certainly vs. Ruby/Python/etc. For extremely mission critical code, this is fine, but for most startups I would argue it probably isn't appropriate.
Definitely staying tuned as Zig develops.
I was writing a emulator (and later: a compiler) in Zig which was originally written for PC. But i got the idea that hosting this stuff on the web page would be cool, so i learned how to do Wasm. The result was for both project a glue file with ~150 LOC Zig and ~150 JS and both compiler and emulator ran in the browser, and porting both projects took less than an afternoon of time.
Zig is a better C and C++. It should be used accordingly. It will do well in game servers, simulation servers and real-time systems that don't require hard safety constraints. Bonus points for Zig, it is a simple language and because of its nature it will be easy to build tooling around it to prove properties.
That's a bold claim. What's the C formal validator which automatically handles both memory management and concurrency in source of any size within seconds/minutes? (Without making the source its own dialect rather than C)
Anyway, you can verify the critical part of your C/Ada program by using: Why3 http://why3.lri.fr/ Frama-C http://frama-c.com/ (which is also extensible) SPARK https://www.adacore.com/about-spark
One company that I've worked for used generators, they were specifying the model with a DSL and they generated the code based on that. Can't give more information about that but there are others doing the same (SpaceX and NASA). Rust is very good for people that don't have the resources and money to throw at or are working in an industry where they don't need a certification, for example I have friends at Amazon in Romania that build Firecracker, a virtual machine that is supposed to improve the safety story on AWS Lambda.
And as an answer for your second question, at what cost? Also we don't know if Rust gets the scaling right. The compiler is already slow for the size of projects we already have.
Rust is brilliant, but for drivers, I would go for a language with OOM safety and strict static allocation, especially for embedded environments.
There a GC'd language with modern features should do best. Imagine OCaml but modern and great tooling. That would be easy for developers, more productive to write, less type errors, also more productive because of IDE support, and much faster than current crop of scripting languages.
Sadly, there is a vacuum for such a language. Go is too gruntwork and minor details, Rust is designed for high reliability system programming, Zig is designed as sytem language in spirit of C, OCaml is archaic and does not seem to improve by much.
The hopes in this area are
Nim - Nice python-like syntax, but feels a little unpolished, metaprogramming may be hindrance to IDE tooling and code readability on large codebases.
Crystal - Ruby like syntax and stdlib. LLVM compilation, very young language, no windows support, and (personal opinion) I think some work can be done on performance of idiomatic code.
OCaml - there is not much manpower behind it. All those Reason XYZ attempts to provide javascript syntax over it don't seem to have gotten traction. Tooling is pretty good considering how obscure language is. They might need a modern interface to toolchain, and an optimizing compiler seems to be being worked on. La k of multicore is often cited as a drawback but it is being worked on, and Python doesn't do multicore either, I don't think multicore matters to 90% of people doing webdev.
F# - Would be nice if it was not confined to .NET ecosystem and had good native compilation story.
I predict that there will be a paradigm shift away from GC in the next round of languages. I suspect what will win for something like web-dev will be a language with static memory management like Rust, but at a higher level, with slightly more tolerance for abstractions of non-zero cost.
There's still a market for more performant and predictable networked services. It's a bit too early for a full-fledged post explaining the feature in detail, but as far as I know Zig is the only language that can do async/await and at the same time ensure that when memory limits are reached, the system still behaves correctly (i.e. you can preallocate upfront the memory you need to instantiate a coroutine and, if that fails, you can gracefully return a 500 http error code).
Serious webdev is out there, and when SREs talk about the importance of predictability and low-variance in metrics, they aren't (just) writing content for marketing purposes.