Older card sets retired to the 'Wild' format in Hearthstone [official site] will soon become purchasable again, Blizzard have announced. Wild is format where all cards from every set are allowed, the one Blizzard created in 2016 to create a rolling metagame in the 'Standard' format with limited sets - and to make Hearthstone friendlier to new players. Blizzard had stopped selling cards for expansions only in Wild, but that made getting into Wild a faff for newer players who wanted to get into it. That'll change "in the coming weeks", when they all return to sale.
Blizzard's blog says it plain and simple:
"If you yearn to return to the Wild, we have some good news for you!
"In the coming weeks, ALL Wild sets—including Expansions and Adventures—will once again become available for purchase on the Blizzard Shop at https://battle.net/shop/product/game/hearthstone!"
If people want to get cards for Wild play right now, they need to craft them individually. Buying packs is simpler, more generous, and more fun.
However, one thing Blizzard are slightly hazy on are whether they'll only be buyable with real money or, like other sets, also with the fake virtuacash earned by playing. The Blizzard Shop only accepts real money, but Blizzard only mentioning that could be a clumsy plug for the Shop or... it's not clear and Blizzard haven't clarified yet.