Epiphany! I know how this is all going to play out. It's my Hari Seldon moment.
OS 10.7 introduced several features and styles from iOS. Launchpad for example.
OS 10.8 includes additional rich iOS features (Notifications Center), and some clever iCloud synchronization with Apple’s iOS apps (Notes, Reminders).
2013/2014 - OS 10.9 will take this even further of course; especially synchronization. Perhaps this means universal apps will appear in both the Mac and iOS App Stores, and be compatible with both operating systems.
2015/2016 - OS 10.10 will be called iOS. There will only be one operating system, and it will run on all Apple products. iPhones, iPads, and iFutureDevices will connect to external displays, and will support input from keyboards and mice.
Think about that for a minute. Imagine docking your iPhone, and using iOS on a large display. Browse the web, answer emails, chat, update your Globenet status, etc. Then when you’re ready to leave your house, grab your iPhone and walk out. What does this mean for laptops and desktops? They’ll still be around, but basic computing needs won’t require them anymore.