Mandatory explicit initialization, plus a feature to explicitly mark memory as having an undefined value, is a great way to approach this problem. You get the benefit in the majority of cases where you have a defined value you just forgot to set and the compiler errors until you set it, and for the "I know it's undefined, I don't have a value for it yet" case you have both mandatory explicit programmer acknowledgement and the opportunity for debug code to detect mistaken reads of this uninitialized memory.

But I think it would be troublesome to use such a hypothetical feature in C if it's only available in some compiler-specific dialect(s), because you need to coerce to any type, so it would be hard to hide to hide behind a macro. What should it expand to on compilers without support? It would probably need lots of variants specific to scalar types, pointer types, etc., or lots of #if blocks, which would be unfortunate.

Zig is a nice language with this feature, and it fits into many of the same use cases as C: https://ziglang.org/documentation/0.9.1/#undefined