Hmm. Not very keen on this. A lot of blue Illusions are undercosted things that go away if the opponent targets them. But I think more decks will have the ability to target than have the ability to draw extra cards. Especially with pseudo-draw like Act on Impulse, Raise Dead or Fact or Fiction not counting as real "draw" for the purpose of this card.

How about something like "When an opponent has six or more cards in hand, sacrifice ~"?

I don't know. Maybe it's just a bad idea for a drawback. In my experience a red or white deck that slips down to two or three cards isn't ever going to pop back up to six. All it takes to get rid of it now is a cantrip, but you're right that unequal access to card draw among the colors makes this awkward.

I reduced the toughness to 1. Blue can definitely get a 2/1 for , so with a rarely-met drawback, perhaps it can get a 3/1.