So I'd say that's case closed on why 4k wasn't offered.
Well.... yes and no, first of all I can't comment on the ATV because of the NDA, but we can talk about the A8 chip performance in iPhone 6 form.
While my last answer was intended to be a bit at the limits (and a bit tongue-in-cheek), the reality is, with iOS games they're never exactly trying to compete on a like-for-like with consoles and PCs.
So, here's an honest answer based on just the A8 chip, not, just to cover me arse, the new Apple TV.
The A8 can play back 4K video content without breaking a sweat so Apple could have (and indeed could via software in future I guess) enabled 4K video playback. My guess is they didn't because iTunes 4K content simply isn't there yet, they need a selling point for the Apple TV 5 and neither is the customer base of a significant enough size, yet.
But with 4K TVs becoming ridiculously cheap, this will change over the next couple of years as we all decide we want new tellys (I've been eying up a nice 4K OLED for a while, but considering I just spent 2 and a half grand on a telly last year, the wife will need to be sent handbag shopping before I can sneak one of those in, anyhooooo, I digress (so unlike me

))
As for games, well, the maximum internal resolution iOS games are currently rendered at is about half the resolution of 4K. Or at least I should say, that's the maximum resolution were allowed to publish a game at. What games choose to put that to full use and which ones use a lower rendering resolution for performance is pretty much anyones guess.
I've been playing around a little and yes, I can force games to render at 4K resolution internally with a smooth frame rate. You could theoretically do a decent 2D game at 4K and some simpler 3D ones. But clearly we're not talking about seeing GTA 5 in 4K on an Apple device (other than a Mac) for a few years yet. But it will definitely come, I wouldn't be at all surprised if the iPhone 7 or 7s started to usher in 4K gaming.
You need only look at games like Need For Speed No Limits, Breakneck, AG Drive, the upcoming Rayman Adventures to name just a few (all of which I think look pretty good) to see just how far mobile gaming has come in a short space of time. Think what another year or two will be like.
Of course, I'm often wrong, I blame my copious amounts of medication for clouding my judgement, speaking of which, time for my morphine. My next posts may go even more down hill
