"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Tickets for WWDC 2013 Sell Out in Two Minutes
WWDC has sold out increasingly quickly in recent years, and this year in particular saw a massive rush of developers ready to purchase at the launch time due to Apple having announced the on-sale time a day in advance. Previously, Apple had begun sales at the moment it announced details on the annual conference, but with last year's tickets selling out in under two hours, some developers found themselves out of luck before they had even woken up for the day.
WWDC 2011 sold out in under 12 hours, while the 2010 edition took eight days. This marks the sixth straight year that WWDC has sold out, a streak that began in 2008.
With the increasingly quick ticket sellouts, there have been calls to increase the size of WWDC. Apple would, however, be hard pressed to do so given that a major focus of the conference is on assisting developers with their apps and Apple needs to have enough engineers on hand to provide that hands-on help.