When I import a hi-res video file in 2560x1440 (16:9, WQHD), the preview display for the images is skewed, and exporting options are only available for a 4:3 format (960p, 1440p and 2.7k). The exported files then have added black bars at the top and bottom (letterboxing). It seems that the program is treating anything with a height of 1440 pixels as a 4:3 format, regardless of the actual aspect ratio of the file imported.
2560x1440 is pretty useful, since it allows for the next quality "step" in Youtube (1440p), offering a higher bitrate when viewing the video.