Battery life would be terrible. The only way that would work, with reasonable battery life is for an ARM Processor. You'd get, maybe, 3 - 4 Hours of battery life, not to mention the weight and design of this would be completely impractical. It'd add thickness, and weight. You'd be much, much, better off just getting a MacBook of some kind.
I could see them making iOS much more powerful and useful by adding certain elements from macOS. I could even see Apple going so far as to allow Magic Trackpad to work with iOS. I could see the Apple Pencil being used on macOS via TouchPad in the future. I could also see better integration between macOS and iOS and iOS being a 'Second Screen' much like DuetDisplay.