In announcing the dates for WWDC (it starts June 2 in San Francisco and consistently sells out quickly) Apple made clear it will discuss its plans for both iOS and the desktop OSX.
"At this year’s five-day conference, developers from around the world will learn about the future of iOS and OSX …." Apple said.
Keep in mind this a developer's conference, so if iOS 8 is shown it will be to give developers a running start creating apps for it, the OS itself isn't likely to be publicly available for download until the fall.
Several new features have been rumored to be coming with iOS 8 including a new app called Healthbook that will turn your iPhone into a fitness and health tracker giving the ability to monitor your vital stats.
Apple is also expected to show off a new mobile payments service, as well as improved versions of Maps (where there's clearly nowhere to go but up!) and Siri.