It wont happen
As mentioned their SDKs are very expensive
Also, i don't see any way tablet or phones could replace dedicated gaming handhelds
My Sony tablet is lovely for what it is but it could never compete against a Vita or 3DS
Physical buttons, flash cards, analogue sticks and top quality games is what separates tablets and phones from dedicated gaming handhelds
Finally with current battery tech i'd absolutely hate to have one more use for my smart phone. It barely holds battery through the day as it is, i can't imagine gaming on it for longer stretches as well