Depending on the chip and GPU inside any new Apple TV -- which hasn't seen a refresh since January 2013 -- Apple could later add 4k video support, so all isn't lost if you own a new 4k TV. Most people don't yet, however: Although 4k TV shipments are rising quickly, they're still a very small portion of all televisions sold. DisplaySearch estimates that only 6.4 million of the televisions shipped in 2014.
That's a significantly small portion of the total number of television sets around the world. So while 4k TV owners may be vocal about wanting a new Apple TV to support the higher resolution format, there simply aren't enough of them to influence the market.
Apple tends to aim for the lowest common denominator type of consumer by making products appeal to a wide range of potential buyers. Sure, it could easily add 4k support to a new Apple TV, but with relatively few television sets actually capable of using it, why add it and then market the feature to such a small demographic that can use it?
It's far more likely that any new Apple TV launching this year will be focused on a new app and interface experience, along with cord-cutter subscription models that can help consumers break away from their cable or satellite provider.
We've already seen evidence of that with the new HBO Now package coming this month for $14.99 on Apple TV as a limited-time exclusive. And separating themselves from cable companies is what more consumers are interested in; 4k support can always come later -- once there's more content available -- and be icing on the cake.