I was hoping Apple would have done this by now, but I don't think that's the direction they want to take. If you need that type of flexibility, you're probably better off with a MacBook Air.
I do have Macbook Air, even 2 including my wife's, both i5. It is excellent computer which at home is used with with a 22 inch Acer monitor. I have experience of working in desktop publishing industry and have some knowledge of Illustrator and Photoshop (mainly technical illustrations), but I would like truly to draw on iPad. However, without the sensitivity levels of Wacom, its not very much useful.