I'd be interested to see an actual implementation of such an allocator in Rust that exposed a safe interface. You could do it in the specific case of chunks of predefined sizes, and maybe even for all byte arrays, but to allow arbitrary types in the allocator I do not think you could expose a safe interface without requiring initialization.

Again: I'm quite confident you could reproduce this specific vulnerability. You would just have to go out of your way to do it and the benefits of managing a free list yourself aren't really there (jemalloc is quite good at large allocations).