The more they add to the iPad, the closer it gets to being a MBA-like device with a detachable keyboard/power supply/magic cover/etc.
I have an iPad (3) and am underwhelmed by it: not as powerful as an Air, not small enough to be convenient to carry around, slow and handicapped by the limitations of iOS.
I use it a lot (I own it so I might as well use it), but think it is a flawed device.
For me, a MBA and pocket-sized iPad with a useable file system and multi-user accounts would hit the sweet spot.
Oh, and one with 4G that works outside of a handful of countries. I bought my "4G" in the UK and was told twice by Apple Store staff that it would work with UK 4G. Apple's customer service for the iPad 3 has been lamentable.