The real problems start when you need to manage memory lifetimes across the whole program, not locally. Can you return `UniquePtr` from a function? Can you store a copy of `SharedPtr` somewhere without accidentally forgetting to increment the refcount? Who is responsible for managing the lifetimes of elements in intrusive linked lists? How do you know whether a method consumes a pointer argument or stores a copy to it somewhere?
I appreciate trying to write safer software, but we've always told people `#define xfree(p) do { free(p); p = NULL; } while (0)` is a bad pattern, and this post really feels like more of the same thing.