Microsoft made an announcement during E3 this year that even surprised the PlayStation CEO, they confirmed the existence of Project Scorpio. The next Xbox console will be quite powerful compared to the current Xbox One build, it has been detailed to feature eight cores, six teraflops, 320GB/s memory bandwidth, 4K/VR gaming, backwards compatibility, and will be available in 2017.
As far as 4K goes, Microsoft detailed that the console wil have true 4K visuals and VR quality that wouldn't be held back by the console's hardware. While the console was specified to feature 4K resolution, it won't be mandatory for games.
According to Xbox head Phil Spencer, Microsoft will not "mandate 4K frambuffer."
@ThatDudeizEric We'll talk more about this later but we never said we'd mandate 4K framebuffer, we won't.
— Phil Spencer (@XboxP3) June 20, 2016
This means that games could ship for Project Scorpio at 1080p resolution then be scaled to 4K, which could allow Xbox One games to be upgraded with better graphics for the new console.