I'm not exactly sure what's happening over at Blizzard, but whatever it is I am definitely in favor of these pro-customer moves. The Overwatch devs have just recently announced that the previously extremely unfair Loot Boxes will be transformed into something quite amazing, and now we are getting the exact same announcement from the Hearthstone developers as well.
Starting with the release of Hearthstone's next expansion (though this applies to all card packs), every time you open a Legendary card you will be guaranteed to receive a non-duplicate Legendary card from the same set! This works for both golden and non-golden cards, so don't worry getting duplicates just because you like to have your Legendary cards extra shiny.
Furthermore, with the release of the next expansion you are also guaranteed to get a Legendary card within the first 10 packs of the new set. This alone might not sound like much, but when combined with the above-mentioned changes it should result in your collection growing by quite a large margin, and with it the amount of competitive decks you can create. Again, I'm not sure what exactly prompted Blizzard to do this given that Hearthstone is constantly bringing in ridiculous amounts of money, but I certainly won't complain about them finally moving towards a more player-friendly system!
If you're interested in all of the details, though there really aren't that many, you can find what you seek on the official website. If you would like to hear all of this from Ben Brode himself, allow me to send you off with the recently posted developer update video: