I think what he's getting at, which I agree with, is that a lot of people think they want a converged iPad/Mac, but if Apple actually came out with it, people would not like it since it would be a compromised experience.
ARM isn't fast enough to emulate x86 to run old Mac software, and it isn't fast enough to power the iMac or Mac Pro, so Apple would be unlikely to force OS X developers to go through another architecture conversion. On the other hand, Intel processors aren't efficient enough for iOS. The closest is the Core M, and ARM actually outperforms it. Apple would need to emulate ARM on Intel in order for iOS apps to run, which would hurt performance and battery life.
Plus, OS X isn't optimized for touch, so there would be a huge risk of a Windows 8 issue if Apple tried to force touch onto a 15 year old operating system designed for mouse and trackpad input.
Not if the end result looked like Windows 8. Even Windows 10 isn't ideal, particularly since Desktop software doesn't run well in touch mode, and developers aren't rushing to develop Metro apps. Plus would this OS X tablet run iOS apps? See above.
What processor would you recommend Apple use for the MacBook? The MacBook Air processors use up too much power (so it would be more of a Surface Book, which weighs as much as the MacBook Pro). ARM doesn't run x86 software natively, and would be even slower than the Core M if Apple tried to emulate x86.