The Hearthstone folks posted yesterday about some card changes that are coming with the next major release, version 5.0. The exact patch date wasn't specified, but the Whispers of the Old Gods set release was announced for April 26, so it'll be sometime between now and then.
I'm glad that Hearthstone has generally avoided the first approach. Creating new cards that counter powerful problem cards almost always creates new problems. A perfect example of this was the 7th Sea card game from many years ago, which had a few very powerful cards that almost everyone used (most notably Betrayal). Quite a few cards were later printed that could stop Betrayal, but that just meant everyone had to use those. Working around the overpowered cards, instead of just nerfing them, meant the designers were limited and deck construction was more difficult.
The set of changes announced by Hearthstone yesterday fall under the second approach: reduction in power level for the cards affected. Some are fairly minor, such as reducing Knife Juggler from 3 attack to 2. Most of the utility of Knife Juggler comes from its ability anyway, not its ability to attack. Others are larger changes, like the update that both increases the cost and reduces the effectiveness of Blade Flurry. In the current environment, several of the larger changes seem to make the cards pretty useless for constructed play, but that could always change as new cards are released.
Hearthstone is also using the third approach, by adding the Standard format. Once Whispers of the Old Gods is released, there will be two constructed formats. Standard will use only cards from the current and previous calendar year, plus the basic set. That eliminates expansions from two or more years ago. There will still be a format where all cards are legal, called Wild, but I expect balancing efforts to focus almost entirely on Standard.
I'm glad to see Hearthstone is keeping the game fresh by limiting the card pool (for Standard format, at least) and reining in powerful cards. I don't actually play constructed all that often, preferring Arena format or Tavern Brawls, but when I do it's nice to see a variety instead of the same powerful decks over and over again.