The Swedish Cyberphoto site posted that video from the Fotomässan 2015 show. And you can see the Leica 100-400mm size very well. It’s really not that big!
And this comes from Martin: “Panasonic 100-400mm size size comparison. I thought this was an interesting comparison to the 40-150mm PRO. http://www.dpreview.com/forums/post/56779139”
The lens will cost around $2,500.