XB is still only 20 years old. We need to see how he does in the postseason, but it might be worthwhile to let him marinate in the minors in 2014 and push his arbitration clock back a year. If Middlebrooks is ineffective, Drew/Pedroia gets hurt, or if their 1B plan doesn't pan out, they will have a very good depth option.
I am also not convinced that Drew is going to want to be a backup plan in 2014, even if it is a 14 million check in his pocket. Boras will probably see this offseason as the last chance for Drew to hit it big. He'll be 31 next March, and if he loses playing time to injury or being bumped out of the lineup, he probably won't ever see a multi-year deal again, nevermind an 8 figure deal again.
The reason why this year worked was because BC made smart, flexible deals that built depth. If Drew takes the QO it will be exactly that.