We're waiting for a little more market saturation of 4k. Not just cameras, but TVs, monitors, and yes, mobile devices that can actually view 4k content. For example, an iPhone 7+ has a screen resolution of 1920 x 1080 pixels. 4k resolution is a stunning 3840 × 2160 pixels. Right now, all 4k would do is make 1SE files even larger. Which would be a major problem for many of our users.
Once 4k becomes more prevalent we'll support it.