I think an iPad Pro 12.9" with the new Magic Keyboard and a suitable amount of storage (at least 256GB) would be perfect for most people. Screen size, processing power, portability, battery life, it hits almost all of the buttons. Except one.
Unfortunately, today, the price of such a beast is well into 15" MacBook Pro territory, and that puts it out of the range of what I think the average person is willing to spend for a computer that’s not a full-fledged notebook.
When you can buy an 12.9" iPad with a Magic Keyboard for the price of an MacBook Air today, then the combination will be “perfect” for almost everyone.