I think it's possible that one day you could hook your iPhone/iPad into a monitor and get the same iOS, but with obviously a lot more screen real estate, multi windows, etc. This is a bit of a stretch, but certainly possible. I think Apple will continue to add macOS-like features to iOS for iPad and continue to expand on it's capabilities that way. That's the more likely, and better move in my eyes. iOS already surpasses macOS in a lot of ways for me, I'd rather them stay on that track. We'll see though.