The iOS will absolutely change. At the minute the iPhone was introduced, it was obvious that the hope of future devices would be a single OS to cross all platforms/form factors.
Microsoft has taken the first step, and having never played with anything more than the Windows phone for a few minutes, it appears that they have made the first move in consolidating OS's across devices. We would be amazingly foolish to assume that Apple is not moving in that same direction.
iCloud is the first step to allow the devices to talk, regardless of current OS. That I would predict will first expand to other apps (such as the iPhoto app for iPad/iPhone being able to sync perfectly with its mac counterpart), and eventually to all files (music, videos, documents, and file systems).
Finally, the last step (and by far the most radical) will be a HUGE introduction of a new Mac OS that will, in some form or another, be exactly the same as the version seen on the iPad/iPhone.
There will be some things that will remain different (such as the size of the "stoplight" buttons on the top left), but as the average consumer becomes more knowledgeable about how to use complex devices, then more complicated operating systems may be introduced. Since the general population knowledge on using computers will be heightened, it will be easier to introduce more and more complex systems. They will still be simple to use, but will be more and more layered (in a good way).
Anyway, yes, they will change it drastically. When that happens, I have no idea (no one outside of Apple does). But it won't be iOS, it won't be Mac OS X, it will be something else.