Just a brief note: Andrea Tornielli, one of the most well-informed vaticanisti, reports that the Pope is going to send a letter on this matter to the world's bishops. Here is his short announcement in an NLM translation:
Williamson Case: A Humble and Forceful Letter of the Pope to Arrive
Thursday at noon will be made public a seven page letter which Benedict XVI sends to the bishops of the Catholic Church to address the case of the revocation of the excommunications of the Lefebvrist bishops and the controversies about the interview denying the gas chambers released by bishop Williamson.
UPDATE
This is now confirmed by Paolo Rodari.