Congrats to the zig team! This is a big milestone and they must have put an enormous amount of work into making it happen.

At the same time, the reason this milestone seems so significant is because the language is already quite complex. It seems likely to get even more complex over time. Some metrics of complexity that jump out are the amount of compiler source code, compiler compilation time and required resources (cpu/memory). There are other languages that have simpler and more efficient bootstrap compilers.

Ideally, a self hosting compiler contains only the minimum amount of information that is strictly necessary to compile itself. It is possible to write one for a simple, imperative, javascript style language in at most a few thousand lines of code in pretty much any reasonable turing complete language (something like lisp with barely any syntax can be done even more succinctly). Because the simple language is so small, the implementation can also be written in a high level language that targets that same high level language, i.e. the bootstrap compiler could be a transpiler to javascript written in javascript. There is little point in compiling to native assembly during the bootstrap process because the language is so small that a good javascript implementation should be capable of compiling the bootstrap source in under 200ms on a decent laptop. Once the compiler can compile itself, then one can add more features to it, such as a more robust type system, a native backend or automatic memory management without gc. A positive feedback loop emerges because these features are implemented as optimizations to the compiler itself. It gets faster as more features are added to it but it is always fast because it was fast from the
beginning. With good benchmarking in place, it should never get slower at compiling itself.

Such a compiler/language would be very minimal by design but a more batteries included language can be built on top of it, much like how an os kernel is extended by user space programs.

A historical example of this kind of self-hosting compiler is Forth. It is easy to bootstrap (see e.g. JonesForth). Derived programs are written by extending the compiler with a new vocabulary specific to the problem at hand. Development is often done in a REPL environment for fast feedback. REPL sessions can be saved as source files once the program works as expected. Forth syntax is unfortunately inscrutable to most and the stack based design is not great for every problem so I wouldn't recommend actually using it, but it contains important ideas that can be adopted into more modern languages.

What the zig team has done strikes me as very, very difficult, so I tip my cap for the effort it must have required. In the long run though, it feels almost inevitable that a simpler language with the more desirable high level properties described above will eat its lunch. As painful as it would be, I believe the best thing the zig team could do to ensure the language's long term survival would be to completely rewrite the language from scratch (zag?) using the knowledge that they've gained during their initial bootstrap process to distill zig to its essence.