Yesterday, Microsoft finally announced what's coming in the spring update for the Xbox One family of consoles. Just like its Windows 10 counterpart, it's codenamed Redstone 4, and one of the new features is support for 1440p displays.
First of all, this is limited to the Xbox One S and the Xbox One X. The original Xbox One didn't support resolutions over 1080p, and was never meant to. Obviously, it's not likely that you have a 1440p television that your console is hooked up to, but you could have it set up with a 1440p monitor.
But the Xbox One S and the One X handle content differently on each. When the One S launched, its major new feature was the ability to stream video content at 4K UHD, while the Xbox One X was able to actually play games at native 4K. The One S was still capped at rendering games at 1080p, and that is not changing. Games rendered at 1080p will be upscaled to 1440p, in the same way that they're upscaled to 4K if you have a display to support it.
The Xbox One X will have select games that render at native 1440p. It's not clear how popular support for this will be. Otherwise, if the game has been enhanced with 4K UHD support, then that will be supersampled down to 1440p. And of course, games that still render at 1080p will be upscaled on the Xbox One X as well.
As far as media playback goes, this works differently. Rather than downscaling 4K content - which both consoles are capable of doing - both the Xbox One S and the One X will upscale 1080p content to 1440p.
That's about it. As has been the case on 4K displays, the gaming experience is still better on the Xbox One X with a 1440p screen, and media playback remains the same across both devices.
The spring update is currently in preview with the Alpha ring of the Insider Program, and will roll out broadly in April.