I tend to disagree with this.
The separated thumb keyboard they show is hardly new. It's been done on Android and I remember seeing it on tablet PC's of one type or another over the years. A bigger problem for me is that Microsoft has a long history of pushing "ergonomic" (split, humped, sideways) keyboards and they never catch on with anything but a tiny minority of users. For a touch typist, to separate the keyboard into two pieces means you have to look at your hands when you type and your speed is instantly reduced to a snail's pace.
Im a touch typist, yet even when the iPad is in landscape mode I have to look at the screen. The glass all feels the same to me and I simply don't trust the outcome of my efforts without looking.
Now that you mention the problems with split keyboards, causes me to pause. I haven't considered the additional effort required to continually refocus one's eyes from each side of the tablet as you type. Good point. This could very well be an issue. Don't know till I try it.
Giving this some more thought, I think I would be just as happy with an iphone sized portrait keyboard along either the right or left side of the ipad in any orientation. Either at a user pre-defined location or using some kind of proximity sensor to determine where you are holding the ipad with your hand(s).
Im sure there are plenty of designers at Apple thinking about this issue on the iPad already.
I also agree with you about smaller sized iPads. I think the ergonomics of the smaller unit that you can easily hold with one hand without getting tired would feel nice to me.