"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
WWDC Banner Confirms iOS 6 Announcement
iOS 6 has been assumed to be a major topic of discussion for the event, but Apple has so far mentioned only that it will discuss the "future of iOS" at the event. The banner also displays a silver-colored theme that has been rumored to making its way to the iPhone to replace the blue theme present in many of Apple's apps. The silver theme has already been showing up on the iPad, but rumors of an Apple mapping app have suggested that the silver theme will moving to the smaller screen as well.
With Apple having dropped numbering and other descriptors from its latest model of the iPad earlier this year, there has been speculation that the company may follow suit with other products such as the iPhone. Today's banner indicates that the company will at least continue marketing iOS using its version number.
Update: A clear shot from CNet:
iOS 6 icon cropped from CNet's image shows the background is water ripples: