As far as I know at least part of the idea was to eliminate the function coloring problem by letting the compiler do some nifty compile-time deductions. This had some issues (I don't know if this is still planned, it seems like the kind of thing that should not work in practice). Additionally, there were all sorts of hard technical issues with LLVM, debugging, etc.

I recommend checking the issue tracker, eg. https://github.com/ziglang/zig/issues/6025

I personally don't understand the domain well enough at all, but honestly, I feel like (if possible) Zig should try to double down on its allocator approach.

Instead of trying to use some compile-time deduction magic explicitly pass around an "async runtime/executor" struct which you explicitly have to interact with. Why not?