I would love to see a mode (particularly for replay observer) where the entire UI can be toggled off (playback controls, annotation controls, all of it), so that the video can be larger on the screen and be free of distraction.
Related: there seems to be a minimum width for a playback window? My video files are 1280x800, but I rotate them all into portrait orientation, but cannot shrink the window smaller than 1187px overall width. If I set windows scaling to 100% instead of 125% (I have a high-dpi screen on my laptop, so this is not ideal), I can get the window to 950px minimum width. This still leaves blank space left and right of my playback videos. I use Kinovea for playback of golf swings, and it would be nice to be able to fit 3 windows on one screen, but with this minimum window width issue, that doesn't seem to be an option.