Unofficial Apple spokesman John Gruber has written a short post on Daring Fireball suggesting that iOS 7 is running well behind schedule—and that as a result Apple is hauling man power from its OS X development team.
iOS 7 would typically be ready for the Worldwide Developer Conference, which is now just months away. Gruber explains:
What I've heard: iOS 7 is running behind, and engineers have been pulled from OS X 10.9 to work on it.
If that's true, it wouldn't be the first time Apple has had to transfer devs to work on iOS rather than OS X: back in 2007, Mac OS X 10.5 Leopard was delayed by four months to ensure that the iPhone project was ready on time.