Making it opt-in, means making the hierarchical approach the default. Whatever you make "opt-in" means you are by default discouraging its use. And what you are suggesting as the default is not what I wanted from Odin (I am the creator by the way).

I normally say "try to make the zero value useful" and not "ZII" (which was a mostly jokey term Casey Muratori came up with to reflect against RAII) because then it is clear that there are cases when it is not possible to do ZII. ZII is NOT a _maxim_ but what you should default to and then do something else where necessary. This is my point, and I can probably tell you even more examples of where "ZII is bad" than you could think of, but this is what is a problem describing the problem to people: they take it as a maxim not a default.

And regarding pointers, I'm in the camp that nil-pointers are the most trivial type of invalid pointer to catch empirically speaking. Yes they cause problems, but because how modern systems are structured with virtual memory, they are empirically trivial to catch and deal with. Yes you could design the type system of a language to make nil-pointers not be a thing unless you explicit opt into them, but then that has another trade-off which may or may not be a good thing depending on the application.

The Objective-C thing is just a poorly implemented system for handling `nil`. It should have been more consistent but wasn't. That's it.

I'd argue "correctness" is important in games too, but the conception of "correctness" is very different there. It's not about provability but testability, which are both valid forms of "correctness" but very different.

And in some non-game applications, crashing early is also a very bad thing, and for some games, crashing early is desired over corrupted saves or other things. It's all about which trade-offs you can afford, and I would not try to generalize too much.