It has been reported that B16 says his private Mass according to the 'Tridentine' rite, and rumours have been rife for ages that he was planning to free restrictions on its use.
Now it's here - the 1962 Mass (most recent revision of the ancient rite) is available to any stable parish group who requests it, regardless of the stance of the parish priest or bishop.
Will it divide the Church? Put the clock back? Force practitioners of tambourine and guitar to seek counselling? Will women have to wear dresses and mantillas or get turned away? What will the Church liberals say about it - and will anyone care?
Or will it bring back dignity, reverence, beauty and fine music back into worship? Will teens in jeans stand beside men in suits with no one minding, because all the attention is on the altar?
Or will the Motu Proprio have little effect on liturgy - be a temporary fad, then largely ignored?