PCGames.De reports that Diablo 3 Game Director Jay Wilson will hold a 30-minutes press conference and Q&A at the end of GamesCom 2010 — in Cologne, Germany — to reveal invited journalists a new secret feature of Diablo III.
The Diablo III demo will be available at the game floor throughout the GamesCom event.
Bashiok seems to confirm this report by the german site.
I wouldn’t be surprised at the fifth class – I’m expecting Heart of The Swarm at blizzcon.