Re: Loss of freedom
>The more the interface is going to rely on this new selection option, the less you can do while holding the tablet in your hand when you're standing.
From watching the video, it is obvious the main envisaged use case is when a person is using their fingers to prop up the tablet and so the thumb is free to move, so to some extent your concern is valid.
However, with a tablet such as the ipad when standing you hold the tablet with the fingers on the back and the base of the thumb on the surround, leaving the thumb free to either provide a third point of contact and stability control or to perform simple actions like pressing the single home button.
So I suggest, provided the thumb controls are kept very simple, like the mouse with 1~3 buttons and possibly a slider/scroll bar, I think they will add to the UX.
Additionally, the use of a handle (https://forums.theregister.co.uk/forum/containing/3173028 ) through which a hand can be placed and thus enable the back of the hand to be used, would permit the fingers to use simple controls placed on the back of the tablet. This however, whilst probably useful to someone standing using the tablet, would make using the tablet on the lap possibly less comfortable.