So I can't seem to find an answer to this anywhere. Is the physical copy of Heavensward just an expansion, as in need to also buy the main game, or is it an all in one main game + expansion?

Like, I want to add a license to play on PS4 but if Heavensward will be both the bace game and expansion, I'll wait till it comes out to add. But also thinking about new players, if I want to get some friends to play I would hate to tell them they have to buy the game twice to play in the new content, but if the expansion is an all in one deal, then it would be easy to get them setup and going.