James MacMillan's new Mass will be sung in Coventry as well as Glasgow. This follows his earlier report on the rather depressing proposals for the music at the Pope's Mass, concluding with the sound observation, "The Coventry Mass should be one that makes the heart soar, not the toes curl."
The new Mass by James MacMillan is a setting for the words of the new ICEL translation. It is not clear yet whether the Holy Father will himself use the new translation at the Masses in Glasgow and Coventry.
Fr Blake discusses the question of Jumping the gun with ICEL as has Fr Boyle. Fr Blake's post on ICEL: Ad Experimentum makes interesting reading. I would have thought that a Bishop in his own diocese has competence to authorise the use ad experimentum of a text that has received recognitio from the Holy See.
In fact, the new translation is being used all over the place at "special" gatherings, by Bishops, by particular communities, and by some individual priests. It does seem sensible for people to get used to the parts of the Ordinary of the Mass that are said by the priest: the responses for the people could later be introduced at the same time across the country to avoid confusion.