That question presupposes a particular compiler implementation of designated initializers. Indeed, C90 had the fixed-order requirement until C99 decided this was unnecessary and removed it.
> Well, consider what would happen if you had members whose value depends on other members.
Can you specify a designated initializer in that way, though? Either you specify a value, or you don't; I'm not aware of a way to introduce dependencies between members with a designated initializer. Yes, you can add a default initializer to a specific member, but that only kicks in if it's unspecified by the designated initializer.
With a constructor initializer list, sure, you can absolutely introduce dependencies on previously-constructed members. But that's not the case with a designated initializer.
Well, consider what would happen if you had members whose value depends on other members. For example, one member is a pointer to another. Or perhaps one member uses RAII to hold a lock and another controls a resource.
Deterministic construction and destruction order is a fundamental feature of C++. Calling it clueless is just an indication one does not know C++.