The compiler’s representation of an uninitialized lvalue might not be observable as the article describes, but an uninitialized heap allocation from the OS (i.e. malloc()) is observable by design.

Of course a language and its clever implementation can make reading unintialized values from malloc()‘d objects UB with all that implies, but that’s a spec choice.

So I believe you could define what’s returned by malloc() as safely castable to one or more “fully mapped types”, which would solve the problem for vectors at least of those types.