In fact one of the reasons for microsoft making that abomination of an os windows 8 was because they thought apple was very close to coming out with a os with ios and osx combined together.
Combining osx and ios together would make a lot of sense for apple because osx lacks games while ios lacks serious programs for content creation. Putting the two together will give apple the perfect os for content consumption and content creation to better take on windows.
when you consider that valve will be coming out with a linux based os to play steam games and microsoft shutting down gfwl, there is getting less and less compelling reasons to own windows. Even programs like ms office and autocad can be found on osx.