> 1. I thought the cast to an rvalue reference would make overloads taking rvalue references be chosen during overload resolution. Since this is deterministic I thought whether something is moved or not would be quite guaranteed

well, take for instance this function :

    my_struct eat_pointer(std::unique_ptr<int>&& x) {
      if(x && *x > 0)
        return my_struct{std::move(x)};
      return my_struct{};
    }

    auto my_pointer = std::make_unique<int>(-456);
    auto res = eat_pointer(std::move(my_pointer));
    // at this point my_pointer hasn't moved a bit
    

sure, this code sucks, but that's always a possibility