The iPad (if MacPad) wouldn't have existed if it were to run Mac OS X. Something that has happened to all the other window tablets.
As far as my opinion is concerned, NO, an absolute NO.
But if we are concerned about the UI, I think iOS 5 is going to borrow a lot from Mac OS X Lion. The premium design has always been missing from iOS. For e.g., the pop-overs, sliders, etc look 'bad' in iOS. I wish they borrow the UI elements from Mac OS X lion and use the same in iOS 5.
It might be difficult for old apps to accommodate those changes but they can always update to the redesign.
As for other features, its a matter of time iOS goes more pro; but Mac OS X is not needed.