The next major version of OS X, 10.10, will apparently be shown off at WWDC 2014, with a number of Apple engineers being diverted to the development team from other projects in order to move the project forward. According to 9to5Mac, OS X 10.10, given the internal codename of Syrah, will form that fundamental basis of the conference, rather than iOS 8, and Apple has been moving iOS software engineers on to the OS X development team so that the new OS can be demoed at the conference.
The new version of OS X will apparently have some similar design influences in common with iOS 7, such as clearly defined white space and more defined icons. Any similarities to iOS will be in design only, in order to provide a more unified user experience across devices, but the report cautions that small design influences is where the similarities will end. The new OS will apparently be released in the Fall of this year, succeeding Mavericks as the Mac operating system.