In Hearthtone, protection against duplicate cards has been added for quite a long time. This means that the kegs will give you cards that you don't have yet.
Have you thought about adding the same system to Gwint, perhaps only for legendary or premium cards? For today getting duplicates of the same cards is very annoying, especially for cards of high rarity.
I know this is an old topic, but I believe it is still a relevant one. There needs to be duplicate protection against legendaries (like in Hearthstone). It is indeed very annoying getting the same card multiple times, only to have to mill it and get 1/4th of its current value. It makes it very difficult for new players to collect new cards.
Update: Due to changes in TWiG's format, this thread is no longer in commission. However,@Burza46 has also embarked on a new podcast, with Flake (the first episode may be found here), and plans to take questions in future episodes. Please, stay tuned for more information.
Thanks to everyone who posted, and my apologies to those whose questions have gone unanswered.