The three finger swipe up would be the same as you do on a Macbook's trackpad on Lion.
The reason for iPad exclusivity is because the iPhone's screen is too small for such. iPhone Multitasking might stay the same.
What are the apps you imagine it displays?....
Better question: Do we need a thumb extension as shown? What software was used for the sketch up?
Not sure of the diagram but convinced of its use in ios6.
I made a better version than your drawing.
Isnt that OS X lion?