Someone actually has to implement the web browser / "tech stack". Web assembly, despite it's name, is an interpreted language. It is not magic. Interpreted languages need an interpreter (written in C).
Because, as the article states, the OS interface is C. In order to do anything useful at all in your code, you need to call through the C API of your operating system.
To replace this, you would need another compiled language. It can't be "any other lang" - it needs to be something compiled down to machine code that can be directly executed on your CPU. So you could write a new OS that presents an interface in Rust, or Zig, but never WASM.
I don't think it has to be C, but it can't be any arbitrary language. It has to compile to machine code, and I wouldn't want to implement a VM in a garbage collected language because you need more fine-grained control over memory then those can provide.
That last requirement rules out most languages with any significant community besides C/C++, Rust, Zig, and a few other even lower profile C replacements.
