Apple evolves its products line by iterating on their design and features. They always did that. I’m still impress by what they do, and the iPhone 5s is a great upgrade to an already very capable device. Look at the smartphone market in general. There are less and less to be done… no more low hanging fruits. This is a maturing market.
I think the next step for Apple is in wearable devices. You may call it the iWatch. Or whatever new name but this is the next thing. I would consider this to be a new hobby though, just like their current Apple TV. This device will complement the iPhone and the iPad and would add to their ecosystem. Thinking otherwise would be risky. I don’t think the iWatch has the potential to become the next iPhone or iPad.
Finally, on the Apple TV itself, I consider TV a dead business. In ten years, cable companies will start to consolidate or die. TV has we know it today is a dead man walking. The new generation is watching content on their device or on the internet. That being said, I consider an Apple TV to be an interesting opportunity for Apple but it has to be focused on content and the user experience. The fact that this device can run apps should be a clear indiction of where things are going: channel will be replaced by apps and will add a new level of interaction with the users: from the content provider point of view and from the advertisers too.