I was thinking this, unless they decide to introduce a retina Macbook Air, they can just do a ''refresh''.
Not sure what they could add to the iPad right now, unless they change some major functionality.
The A8 is more power efficient, so in theory, if they put it into the Ipad at the same clock rate as on the phone, you'd get substantial improvement in battery life. But, they could also boost its clock to 2GHz and make it 50% quicker...