I do think the two operating systems will merge somewhere down the road into, simply,"AppleOS." The trick for Apple will be to make AppleOS as easy for consumers and newbies as iOS currently is, while still offering features needed by power users and creative professionals.
I have to respectfully disagree with this sentiment. The idea that iOS and OS X are converging is a rumor we have been discussing since 2010 and it seems no closer to happening today than it did 5 years ago. In fact, based on Tim Cook's recent comments it sounds like we're farther away than ever. It seems pretty clear that iOS is the future of Apple and OS X will only continue to fade away (with yearly updates to make it better, of course).
I think at the suggestion that OS X needs to be rolled into iOS for it to be a serious computing platform is to completely miss the point. It is to suggest that the ultimate goal of iOS is to become OS X, and that is completely off base. The goal of iOS is to be its own thing. It wants to be better, not just more of the same.
Compare how people interact with their smartphones vs their computers. The average person seems to be more confident using their phone and enjoy using it more. I know tons of people who are a hot mess when it comes to organizing their files on their computer and are afraid they're going to break something every time they use it. These same people are wizards on their iPhones and Android phones, posting to Facebook, sharing pictures on Snapchat, and finding places to eat. These the the moments when you see that iOS (and Android) is not just a simple operating system, but a better operating system.