On my Air 2 you can split-screen in portrait
It's still horizontal spit screen though (side by side). I think they want what I want, which is top/bottom split, so you can have a video take home full width of the top of the screen while another app is on the bottom half. Split that way, each half would be roughly 16:9 and so the video would be a good size. Currently the video is tiny. Even if you do picture in picture it can't get big enough, plus then it overlaps the other app - I'd prefer to keep them separate.