When the Whispers of the Old Gods expansion launched the new Standard and wild formats became permanent in Hearthstone creating a yearly migration of older cards to the wild set. The details of the upcoming standard rotation hit today and Blizzard repeated which card sets were rotating out and also a bunch of new information that should shake things up even further.

Firstly the Blackrock Mountain, The Grand Tournament, and League of Explorers cards are rotating to the wild set. This isn't new news but if you've stepped away from Hearthstone for a time you might not know what cards are going to rotate out of standard. On top of that Blizzard is also moving 6 classic cards to a new set they are calling the "Hall of Fame." The Hall of Fame aims to rotate out certain classic cards Blizzard deems to powerful to stay in the standard set because they seem to limit the design space. Whereas I like each card in The Hall of Fame rotating them to wild does make sense. Nearly each of the 6 cards have no equal and it would be really hard to make cards that are better in some way. The cards rotating to the Hall of Fame are Azure Drake, Sylvanas Windrunner, Ragnaros the Firelord, Power Overwhelming, Ice Lance & Conceal. Again, I get why Blizzard is doing this but the top 3 cards rotating to wild is a bit sad to see. That said they are going to refund us the full dust cost of the cards while allowing us to keep them in our wild set collections. Not a bad deal but i'll miss Rag and Sylvanas in standard anyway!

"We wanted to allow players to disenchant Classic cards that are being added to the Hall of Fame set for full dust refunds, but then felt that incentivizing players to dust their cool Wild cards was counter to our goal of making Wild awesome.

So instead, we're just going to give you the dust, and you can keep the cards!

Up to the maximum number of cards you could put in a deck, we will give you the full dust value of any cards you have that are being added to the Hall of Fame set. (Yes, that means if you have at least one Golden Ragnaros, you'll get 3200 dust!) The dust will be automatically awarded upon log-in once the Year of the Mammoth begins.
"

Originally Blizzard planned on releasing a full expansion, an adventure and another full expansion in 2017 but instead they will release three full expansions.

"Looking back, we learned a lot in 2016 with the introduction of the Year of the Kraken. One of the things we’d like to put additional focus on for the Year of the Mammoth is having additional deck-building options and deck variety in Hearthstone. To help give players additional tools and options to accomplish this, we are changing up the way we handle our release cycle. Previously, a Hearthstone Year alternated between Expansions and Adventures.

For the Year of the Mammoth, our release cycle will include a ~130 card expansion at the start of the year, a ~130 card expansion in the middle of the year, and another ~130 card expansion at the end of the year.

Why the change of release cycle?

At their core, Adventures paint colorful and thematic stories about the Hearthstone universe. Imagine being able to learn about the history and lore behind each of our sets inside the game in a similar way! Defining who the Jade Lotus are through a series of battles between the Mean Streets of Gadgetzan families would have been a great way to supplement the overall Gadgetzan story arc. That concept is something we would like to do more of in future sets: Take the storytelling and cool missions of Adventures, and combine them with the card pools of expansions.

Cards will be acquired via packs like other expansions in the past; additionally, each release will include optional single-player missions that will help develop the expansions’ thematic narratives and offer fun challenges.
"

Blizzard hasn't let us know when the new expansion drops but when it does it will start off the Year of the Mammoth. Since I love all things Hearthstone i'll let you all know when news of the new expansion hits and I keep with tradition a new pack opening video to celebrate.

http://us.battle.net/hearthstone/en/blog/20475356