In addition, Blizzard is introducing ten new cards to the Classic set WOTLK Gold, which will be obtainable through Classic packs or crafting. It says it wants to steadily introduce new Classic cards to maintain a "healthy amount of easily-obtainable cards" through Standard games, as it rotates some out into the Hall of Fame. The studio said these cards will be coming in the next major update, but didn't announce a date.
WOTLK Classic has traditionally introduced a handful of new expansions per year with only minor balance changes in-between. This season the game has been noticeably more active in filling the months between major expansions with other in-game events and changes. After the latest expansion launched in April, its single-player component began rolling out in May, and in June the game issued its first-ever batch of card buffs alongside a brand-new card. You can still claim that card for free by logging in by July 1.
Two more shocking changes are to Baku the Mooneater and Genn Greymane, two cards that were introduced in The Witchwood. Ordinarily Blizzard would wait for cards from an expansion to rotate out on their own, but these two cards--which introduced powerful "Odd" and "Even" decks--have been too prevalent and risk overshadowing the new cards introduced this year. The fan community has been especially vocal about the adverse effect they've been having on the game. Gloom Stag, Black Cat, Glitter Moth, and Murkspark Eel are also joining the Hall of Fame, since each of them relied on the even/odd mechanic from Baku and Genn.
The blog goes on to explain that this year's single-player experience will be one continuous story, with more customization and decks. A free chapter will hit a month after the first expansion, followed by other chapters for 700 gold each, or $20 for the bundle buy WOTLK Classic Gold. Completing all five chapters will net you a special card back and Golden Classic pack.