Youtube support higher than 1080p resolution (normally labelled as "Original resolution" in the menu), which can be 1440p.
However, there doesn't seem to be any really good "live action" video shot and published in 1440p. You will find lots of "upscaled" video.
Your best guess would probably with video game footage, since they can be played at this resolution. But even then it's quite clear that video games developpers aim more for 1080p when they do textures and stuff.