The official website has been redesigned to reflect the change, and most interestingly, Gaijin states that aviation is no longer the title's sole focus. "This name change is significant because the online multiplayer universe Gaijin is developing has evolved beyond pure aerial combat. The massive historical battles featured in War Thunder cannot be fought with aviation alone -- World of Planes is only the beginning," the site says.
What this means is anyone's guess, since Gaijin has not offered any details regarding ground- or sea-based combat as of yet. The company has released a new screenshot gallery, though, and you'll find that and more at the new official site.