In their blog post Anet said they have no plans to add Fullscreen mode for Dx11, so game will always be in Windowed Fullscreen, right now there is an option for Fullscreen but it doesn't actually work while Dx11 enabled, it uses Windowed Fullscreen mode.
As a laptop user, cooling is always an issue for me while gaming, Fullscreen mode helps with cooling while alt-tabbing and away from the keyboard which happens quite often while doing Meta Events. This looks backwards to me that Anet takes that option away from the game.
So, please reconsider adding Fullscreen option to Dx11! or let us keep Dx9 option, although i'd prefer to use Dx11 for performance increases.