Historically,
TV gets hand-me-downs or dual cores with only one working core (or one disabled). It would be a first for it to get cutting-edge.
Plus, existing
TV cores have plenty of horsepower for games. Just because the TV screen is way bigger than an iDevice screen doesn't necessarily mean it has far more pixels to manipulate. If the horses are enough to play back higher-bitrate 1080p, it can certainly work the pixels for gaming. Besides, the way the thing works, it seems it could hand any intensive gaming rendering off to the computer to which it is attached and just stream back the result (of what should be on the screen at the moment).
The h.265 and 4K part is where new hardware would be required. But even there,
TV is usually last in line, meaning expect iPhones and iPads to have such hardware before it eventually lands in
TV. Personally, I don't expect an 4K
TV until iDevices that can shoot 4K have been out for several months. In general, I think Apple sees
TV as almost an afterthought: "oh yeah, now that our iDevices can shoot at 4K, we need to update the little box so that video can be seen at 4K on 4K TVs."