I hope they don't screw it up. The MBA is just about perfect now for what it does. It can't really get much smaller - the screen size and keyboard dictates that. So what could they add/change? Obvious answers are a faster and lower energy processor, bigger SSD size, more memory.
But, I haven't run off the end of any of those three on my 2011 model. Battery life is fine now - I have never had to haul out the mag charger on the road, unless I was gone over night. When I need raw horsepower or massive screen real estate, then that is what my desktop is for.
My main fear is for a touch screen being added to satisfy all those columnists who are claiming that the lack of such shows that Apple has lost the vision. For those I say, go get a Surface and poke all you want but keep your greasy fingers off my Air.