The Warlock ability is tricky. It's the classic 'not everything has the same worth' problem that MTG had in its early days with cycles of cards. Here's looking at you, Ancestral Recall.
There are lot of potential solutions: Make it cost 0 life to 'see' the card and CMC of card -1 per turn in life to 'obtain' it. (IE, 6 cost that turn will cost 6 life, 5 next... 4 two turns later, etc.) Or leave it in hand and put a 2 mana increase cost on it in hand that dissolves after 2 turns or something. But all of them will make it 'not like the others'. Then it starts begging he question: why are all these abilities restricted to 2 mana when the effects are clearly not the same. IE, warrior could be +4 shield until beginning of next turn instead of permanent.
I think down the road, one obvious addition of depth is going to be tailored abilities that change decks and cost various amounts. It seems like the 'simple' way to add a leveling treadmill to the game both to expand functionally (IE, upgrade to 4 mana for 2 damage mage ability) and aesthetically (change mage ability to frost bolt with sparkles for earning some achieve).