As the iPhone becomes more common Apple needs more products for people to buy. They also need more lower priced products so that buying an Apple product is not such a struggle for customers.
An Amazon Echo type device would be great to add to the list. Like the Apple Watch it wouldn't be a product you need to buy, it would just be a product that's fun to have.
More and more people are relying on informal security devices like the Echo to keep track of what's going on in their home. A device like this from Apple would make a lot of people very happy.