Separation of papal powers?

The Catholic Church in Australia got a surprise in a book length critique of Catholicism--from one of the country's most well-respected Catholic bishops. According to The Tablet, Bishop Geoffrey Robinson, retired auxiliary bishop of Sydney, criticized Pope John Paul II for inadequately responding to the sex abuse crisis in Australia and further argued for a "constitutional papacy" that limits the exercise of the papal office and defines the powers of the college of bishops. Some quotes found in the Tablet:

"Papal power has gone too far and there are quite inadequate limits on its exercise."

"We [the bishops] were not asked to vote before the publication of the document on the ordination of women, not even when the Prefect of the Congregation for the Doctrine of the Faith [Cardinal Joseph Ratzinger, now Pope Benedict XVI] spoke of this teaching as ‘infallible', with the Pope [John Paul II] doing nothing to contradict him. If bishops are not asked their opinions even when the word ‘infallible' is in the air, the College of Bishops would seem to have no practical importance in the Church, and the statement of the Second Vatican Council that the college is a co-holder of supreme power would seem to have no practical importance."

As Robinson probably knows because he is a canonist, Paul VI did propose a constitution or basic law for the church when the Code of Canon Law was being revised. John Paul II jettisoned that idea, but perhaps it's time for a rethink. Why not have a "constitution" for the church, even a separation of powers? Why should executive, judicial, and legislative powers rest in the hands of one person?