Would I trade my MBA for this? No, never.
Would I welcome an MBA-iPad hybrid? Absolutely. Why have an iPad and an MBA when you can have both in one?
When the iPad is connected as the screen, a full fledged computer that is exactly like an MBA (Lion, blacklit keyboard, SSD, Ivy Bridge, extra battery life, trackpad, etc).
When the iPad is disconnected, a full fledged tablet that is exactly like an iPad (iOS, 10-hour battery, 32-64GB storage, etc).
Think of the positives - combined batteries for extra battery life, MBA with built-in 3G/LTE, retina display
It would be awesome, as long as it was done right... i.e. seamless and beautifully.