Earlier quoted context omitted.
For the longest time using anything but gcc was a problem. But people found clang/llvm better in many respects and persisted. Today clang/llvm is a drop in option, even to compile the Linux kernel. Similarly we should persist with musl. It’s infinitely cleaner, simpler and understandable.
As you imply, it's not really a standard unless there are multiple implementations. I am in favor of standardizing the behavior of libc and having multiple implementations that are commonly used.
There is already a standard you need to adhere to. It lives one level lower and is the Linux userland-kernel interface i.e the syscall interface.