As of right now all we know is that Journey to Un’Goro will be released in Early April.
There are 135 cards in this expansion and from March 17th we will start to be drop fed some of the cards to look at.
You can pre-order Journey to Un’Goro for $49.99 USD to get 50 packs and a unique card back.
I will add updates as they are released and we know more about this expansion.