It appears on blizzard.com the  splash screen image have been solved, rumors says that there is a rune from Wrath of the Lich King in top left corner.

Beside that Blizzard has acquired Diablo3.com domain from diablo fans.

Its going to be interesting to see what will truly show up on the splash screen 1st july.

Beside that the 1st july is the day where they launched Diablo 2, 10 years ago.