Respectfully, do we really want people to be able to instantly draw Steals, Miracles, Shards of Sacrifice, etc on a whim?
This is an extremely powerful card. It's already becoming somewhat hazardous to not have permanent control in your deck; this card would move it into the realm of the permanently suicidal. Being able to immediately draw whatever card is needed for the occasion, over and over and over? Yow. I suppose this might allow/make it wiser for people to play decks larger than 35 cards, but this could be a pretty big boost to Rainbow decks. (Draw Supernova, have mana for two traces, use one for another supernova, dump card of choice into play.)
This is both card draw advantage AND topdeck-ability. That's a tremendously powerful combination, and for one gravity when upped...yeow.
I don't know if this is a concern, but this would also pose some pretty interesting AI problems in terms of the AI recognizing what to play when.