I think [card[shudderwock[/card] shouldn't be a problem as it comes to late to play to get any value out of it.
taking in consideration, how many good dragons have been revealed so far this card, looks really scary (hello 7 mana Malygos). Versing 8 mana dragon on turn 6 might loos you a game from a get go. I'm far from calling for nerf before seeing this card in play, but we should expect this card being staple in upcoming meta.
The only issue i see is number of dragons you can put in to your deck. The more viable dragons the stronger this card is. If it happens (doubtful) that there will be only couple of viable dragons, only than i can see this card being underwhelming.
After some more thoughts, I'm shifting towards strong but not insane. The main reason that justify this card, is number of dragons in the deck. I cant Imagine deck with this and 29 dragons, not with 20 not even with 15. So basicly card will effect less than half of your cards in the deck.
I'm not switching my vote from meta defying, as i still believe this is the card, that push dragons deck to be viable, but i don't think its busted and insanely op.
Third day and my emotions still shifts to strong, playable card. Shifting encouraging dragons decks, but not as strong as my initial thoughts.