Continued with my Mockup Concept...
A standard 360 controller is just about 6 inches wide, making this controller roughly 8 to 8 1/2 inches wide, which is about as wide as a sheet of standard copier paper. Thus, that's one BIG HONKIN' Controller. The reason for these dimensions is to match the 6" screen size. If you make the screen slightly longer/narrower, you could potentially scale the entire controller inward, making it 6-1/2 to 7 inches wide... which would be comfortable even for big hands. And scale is obviously just eyeballing anyways.
As you can see, it features two Bumpers (Light green) two Triggers (Dark Green), 4 face buttons (in a stylized Gamecube layout; two 'beans', one 'main' and a smaller 'secondary'). Two analog sticks and a D-pad, roughly matching the Gamecube layout. I do think my Left Analog stick is a bit too off-center, but in my mind it kind of feels 'right'.
I also added 3 central buttons which is a feature we've only been able to speculate. Obviously there's a precedent for Start and Select, while a central button could function similar to the 360's 'X' button. Obviously I just made them a generic button style, the central button could be a logo, light, etc.
In retrospect, the Mic might be better positioned on the front for times you don't have the screen up but still want to chat. In theory, the microphone could be built to just pick up voices coming behind it, but honestly... it could go on the front too.
Speakers make sense below the screen, you don't really need those facing you since they're only making a few indicator noises, ala' the Wii.
Obviously the button layout and such isn't optimized for comfort and I have no idea what it would feel like to hold it, but... is there really any news to discuss other than "Hey, maybe it looks like this!"?
EDIT:
Added a fourth controller to show the screen when put in the upright position, and I don't like that
AT ALL. If you cut the speakers and microphone off the screen and just have the screen attached at the hinge, you get this;
Which is much better. I guess since it's just a crappy mockup it's hard to tell, but in my mind the screen is actually behind the Triggers, so the little stabilizing 'fins' on the screen frame (designed to make it fit snugly against hte back of the controller handles) wouldn't get in the way of the shoulder buttons... If you look at the Side View mockup, the screen is actually well behind...
The same effect can be felt by leaning a 360 controller against the edge of a flat surface (like a desk)... in a way, now that I feel it, it kind of gives your index fingers something to 'rest' on, almost like a groove. If they go this route, when the screen is in the up position, the screen frame could be locked in just such a way that it almost BARELY touches the triggers, creative a sort of ergonomic 'groove' for your fingers to slide into.