Unnecessary concern, in my opinion. The Roman Catholic Church has plenty of precedents for retired hierarchs who have the discretion to remove themselves from public ecclesial pronouncements and participate in limited activities, only with their superior hierarch's authorization.
In Eastern Orthodoxy, we likewise have not only hierarchs, but primates, including Ecumenical Patriarchs, who have stepped aside as "Former Patriarch of ____," who do not involve themselves in public critique of ecclesial affairs. (Patriarch Athenagoras' predecessor lived many years into Patriarch Athenagoras' tenure--he passed from this life 6 months before his successor, and only a few knew of his activities, in his private life, except for the seminarians at the Halki Theological School, for whom he was a counsellor, with his successor's authorization.)
The potential exists for a disruptive retired hierarch, but the superior hierarch would have the means to silence such a disobedient hierarch. And Pope Benedict has demonstrated his character of humility and respect for church authority.
As for the matter of the "infallibility," a Pope is infallible when he speaks "Ex-Cathedra," "From the Throne;" a retired pontiff would not have such an ability.