With the release of the next Hearthstone expansion, but still applying to ALL packs, you won't be able to get the same legendary card from a card pack. This applies to crafted legendaries, as well: if you have crafted a legendary card, for example Tirion Fordring, he won't drop for you if you open a Classic pack.
Moreover, beginning with the release of the next expansion, you’re also guaranteed to get a Legendary within your first 10 packs of a new set.
Watch Ben Brode announce this amazing piece of news in his usual excited tone. I mean, what is there not to be excited about?
Lastly, a special promotion is coming soon in the Store. The bundle prices will stay the same, but the number of the packs you will be able to get will be increased. The dates for the promotion haven't been announced yet,