Ok so there's nothing against it currently, but I'm going to need more convincing that it's not inherently dangerous to allow this as a tactic. On the video you can even see a few Sale players look at the ref as they clearly expect the game to stop (I know, they should play to the whistle, but they seemed to recognise that this was a situation where the ref would normally stop the game as it wasn't safe).
As a ball carrier, if you get lifted up to near horizontal you start to become more concerned about coming down safely than securing the ball. I don't care that you know it's the tacklers responsibility to bring you down, you aren't going to leave your neck and/or life in their hands. You prepare for the possibility that you might come down on your head and that involves loosening your grip on the ball.
You aren't allowed to lift legs in the maul and you aren't allowed to play the man in the air, both on safety grounds. I don't see how allowing two defenders to hold a man near horizontal while a third comes in to strip the ball can possibly be a safe way to go.
I'm open to the possibility that I'm missing something, but I can't see the other side of this argument just yet.
EDIT: Simon, btw I disagree about him not going beyond horizontal. I see a couple of times where his head is below his hips and his feet are up. And for me that's why it's dangerous because it's so hard to judge in real time whether the player is teetering on the edge of going over or is under complete control.
