"Tesla CEO Elon Musk offered a big clue as to what "unveil the D" means at Vanity Fair's New Establishment Summit."

States the video description.

Prior to tonight's official announcement, this is probably the closest we'll get to understanding the meaning of "unveil the D" and "something else."

Of note: Elon Musk specifically says that Tesla's announcement will not involve the Model X or the Model 3.