Announced just under an hour ago, Eiji Aonuma showed that the Twili Princess version of Midna will be part of the Twilight Princess Pack for Hyrule Warriors.
Currently the imp form of Midna is playable, using the ball and chain from Twilight Princess. The Twili Princess form, as seen at the very end of Twilight Princess, will use the Mirror of Twilight as her weapon.
Aonuma continued the great news by adding on that this DLC pack will also include new costumes/skins for characters, new weapons, and a new adventure map.
The Twilight Princess Pack will be available on November 27 from the Nintendo eShop.