Mac Observer:

Apple just raised the cap on Apple TV app sizes from 200 MB up to 4 GB, bringing them in line with iPhone and iPad apps. Apple told developers the change lets them give users a better overall experience. For end users, that means more immersive apps and potentially a step towards a 4K Apple TV.

Not “potentially”. Definitely. It’s just a matter of when. I predict at/by WWDC 2017.