Is this really necessary given that the selected item’s velocity vector is both visible on their space bracket AND superimposed onto your ship? This feature enables you to examine their velocity vector even if they’re not in your camera’s view simply by looking at your ship. It’s a great way to visually see their speed and direction. This can be equally or even more useful than a numerical figure since, unlike a number, it scales with the visible scenery and indicates direction. It’s worth noting that your own velocity vector is also shown on your ship, so you can compare your speed and direction with the selected item’s just by looking at your ship.
I don’t think there is any gain from this given the existing feature, but the downside is that the window will get more cluttered.