Wouldn’t gaming require a serious GPU, that hasn’t be tuned for decoding compressed video but packed with parallel processing for rendering shaders? That would add to the already non-trival cost of 4K AppleTV. Also would add to the miniturisation challenge, and as we’ve seen with all Apple products, they’ll happily surrender a truck load of functionality to shave mere millimetres of a products dimensions (MBP, MacPro). Serious GPUs have serious heat management issues.
(Question, in the post-Jobs era does Sir Jonny Ives have too much power and influence of product decisions, given that Cook is clearly not a visionary aesthete and product manager like Jobs he seems to have been given more authority over product (including software now) and a free hand)
Also the Google equivalent for streaming from mobile computing devices, Chromecast is one fifth the cost of a older 64GB AppleTV and at A$99 for the 4K Chromecast Ultra it’s still well less than half the cost of the 4K ATV at A$249. If Apple wants premium pricing it needs to be clearly superior product (in the way arguably iOS is over Android though many would disagree).