In more vague terms, this could be another step towards merging the platforms. How would it be if you had to root your Mac to install software from outside the app store?
Apple To Reveal Future of iOS & Mac OS at WWDC
In less vague terms, this probably means that Apple will unveil a new version of iOS (recent rumors claim it will be a total overhaul of the platform) and Mac OS X Lion, which is due for a Q2 release.
