I don't think Apple is going to sit around and let Amazon take away their "hobby." Heck, after the release of the Fire TV, I would expect Roku to bring out a Roku 4 if for no other reason than to tighten the spec gap.
The Apple TV's CPU is already a couple of generations old. The software can't do audio better than AC3, which is 1990s tech. Apple keeps adding apps, but I think most people would agree with the notion that an actual App Store is at least one of the things the Apple TV needs to grow properly.
It's not going to take a company like Apple a whole lot of engineering time to slap together a new iteration of Apple TV hardware based upon the last-gen iPhone (or whatever), so "it's the software, stupid." That, and content licensing.
What I'm saying is that I expect a new Apple TV this fall at the latest, with radically improved software (perhaps an App Store, perhaps Siri, etc.) and possibly with something new or different on the services side (iTunes video subscriptions, etc.).