We won't see anything this late in the year.
Next year we could see a 15" MBA. If so, I'm a buyer. I believe since Apples announcement that they're now in the post PC era, they will shift the focus from high performance laptops to average performance MBA types that are very thin, light, and be more aligned with iOS, iPhone & iPad lightweight type usage.
For more serious engineering & design work it'll be Mac Pro as long as they exist. Eventually I won't be surprised to see those obsolete and discontinued as the profit Apple seeks is in the mobile space.
Morphing into a mainstream retail company Apple is making too much money to bother with computers. That's another reason the company is no longer called Apple Computer.