Welcome to the forums! And I am glad you are liking Fantasy Express!!
I like that idea and think it is a very interesting idea.
I will take another look at them and see if I can find a way to implement without a major rewrite.
There is already a limit on the amount of Drawbacks a character can take (3 points worth). That won't be going away, but I do like the idea of giving Drive if a Drawback comes into play in a significant manner -- the higher the cost of the flaw, the more likely it should be to come into play (i.e. Lycanthropy is a 3 point flaw, while Ego Signature is only a 1 point flaw).