But to the topic, i dont think OLED are ready to work with the levels of pressure sensitivity yet that the pencil requires. The iPad also already gives top of the line tablet battery life as is.
I also think you'll see OLED being implemented from smaller devices up; since smaller screens are much easier to manufacture with a new tech- so watch (which has it already), iphone, and then ipad.
Agreed on the comment about OLED showing up in smaller screens first. Yields are simply better at smaller screen sizes with newer tech.
As for pressure sensitivity, that's handled by the sensor in the tip of the Pencil, rather than the screen. Force Touch though...