Apple now has everything they need to disrupt the game console industry in a way that none of them see coming. I predict that we’ll see a new AppleTV update (and hardware) this fall along with a new app extension type for AirPlay. AirPlay will become about more than just streaming video to your AppleTV - instead that’ll simply be one of the things you can do with it. Apps (mostly games, I suspect) will be able to bundle an AirPlay extension inside - just like how apps can now bundle photo editing or sharing extensions as of iOS 8. The key difference is where the AirPlay extension app actually executes - instead of running on your device itself from within another host app, the AirPlay extension app will be automatically uploaded to whatever AppleTV you are currently AirPlaying with and will run directly on the AppleTV natively instead. This means no video streaming lag and minimal controller lag. Your iPhone would then turn into a generic game controller with onscreen controls or, if you have a physical shell controller attached to your iPhone, it activates that instead. The game controller inputs are then relayed to the AppleTV and thus to the AirPlay extension app using the new game controller forwarding feature.
Wow. Super fascinating theory.
In my experience, mirroring a game from my iPhone to an Apple TV has been lame because there's always a significant delay between what I do and what I see on the TV. If Apple can solve that problem, this could be a total game-changer for casual gamers. (For hardcore gamers, probably not so much. They'll always stick to their powerful gaming PCs and consoles.)