Blizzard has uncovered the first details of changes coming to Hearthstone. Players will find that "Play Mode" has been renamed "Standard" and includes Friendly Challenges, Ranked and Casual Play. There is no affect on Arena, Solo or Adventure modes.
In Standard Mode, players use decks built from cards from the current and previous year plus all basic and classic cards.
Wild Mode is described as:
In terms of gameplay, nothing is changing for Wild: you’ll be able to finish quests, earn gold, rank up on the ladder, get card backs, earn Legend rank, and use all the cards you’ve already collected to build a Wild deck, just like you always have. When you queue up for Ranked or Casual play with a Wild deck, you’ll always be matched with other players who are also using Wild decks.
The team will be using the next several months re-evaluating cards in both basic and classic card sets in order to make long-needed alterations and adjustments.
Read the full post on the Hearthstone site.