Normally this sort of resource reallocation story leads with Apple taking developers off OS X to finish an update to iOS, but the latest report says that the opposite is happening with development of OS X 10.10: Apple is pulling programmers from development of iOS 8 to finish development of the next version of the Mac OS.
OS X 10.10 'Syrah' has been rumored for some time to include a complete visual refresh, something in line with the iOS 7 overhaul of last year. According to 9to5Mac, that refresh has seen "iOS user interface resources" allocated to the OS X teams so that the work can be ready for preview at WWDC 2014 in June.
The new look will have similar toggle designs to iOS 7, sharper window corners, more defined icons across the system, and more white space than the current version. However, OS X characteristics like the Finder, multi-window multitasking, and Mission Control will not disappear in favor of a more iOS-like experience. Apple is keeping iOS as iOS and OS X as OS X.
iOS 8, on the other hand, doesn't need a complete visual overhaul. There are plenty of items on the plate for the next version of iOS, including a Healthbook app for fitness and health data, a reported breaking into a separate app of iTunes Radio, and apps for Preview and TextEdit. But… that developers are being pulled from iOS to work on OS X means that some of those features might end up getting pushed back to iOS 8.1.
The big news for iOS, however, may very well be what 9to5Mac says "multi-resolution support":
The new iPhone's larger display, as well as a "high-priority" iOS device that is not an iPhone, also lends itself to another core iOS 8 addition. The feature, dubbed by Apple employees as "multi-resolution support," is designed to improve the performance of both App Store applications and the general iOS operating system across multiple new iOS device resolutions.
In addition, there's a reported Apple A8 processor that doesn't make any major architectural changes as the ump to 64-bit did with the Apple A7 processor, instead focusing on speed and battery life improvements.