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I think that it has a lot of potential in a more aggressive warlock deck like Zoolock. It could replace a couple of the more lackluster 1-drops like blood imp or acherus veteran (or patches after april). I'm not sure if you would want to use up a card slot in a control deck for something like that though, since you need a lot of space for anti-aggro cards and late game value plays.

We can at least agree that it's a must for any aggro warlock deck.
However I believe this card will find play in most Control Warlock decks. Right now, Control Warlock struggles in the current meta due to its reliance of its hero power which costs health, something you don't want to lose against aggro. Which is why i believe most control Warlocks will be running the new Spellstone (which I'd love for you to review), which allows Warlocks to survive into the mid/late game due to it dealing 7 damage with lifesteal at full capacity. The only way to upgrade this spellstone is by using cards that make your hero take damage. Since Kobold Librarian offers so much value, it's basically the only way in which you can basically use your hero power, while being able upgrade your spellstone. Plus you get a free 2/1 mana while only costing 1 mana.

Do you think this card solves the issue of taking damage when facing aggro decks? After all, it does the same amount of damage as a hero power, while not offering healing or taunt to resist the aggressive minion push. I think Vulgar Homunculus fits this niche of anti-aggro/spellstone upgrading much better than Kobold Librarian. We also can't forget that cards like Dread Infernal and Abyssal Enforcer should upgrade the spellstone as well! While I agree Kobold Librarian is good value, I think in a control warlock you want 1) late game value 2)anti-aggro (including healing) and 3)demon synergy for Bloodreaver. I don't think Kobold Librarian offers any of these, and draw power isn't really necessary in a control warlock decks. None of the current lists run any card draw because the hero power substitutes for draw cards, not the other way around.