Commonwealth, not superstate? What's the problem with allowing Turkish succession? Obviously, Turkey's imperfect human rights record, and Islamist/NonIslamist fears. What's the good side? It torques off the french desire for a "counterbalance" state, provides a ready model for the rest of the Islamic states, and guarantees that the EU spreads far enough that it cannot form (too much of) an oppressive superstate.
Not 100% sure I agree with all of this, but it's definitely one of the Guardian's better editorials.