There's also other attached documents (apparently put together by the USCCB) after the Motu with some obvious and weak attempts to play down the MP's impact. (see "Ten Questions on the Ordinary and Extraordinary Forms of the Missale Romanum"), and in particular question #5 which not-so-subtly attempts to portray the old Missal as the clearly inferior rite of the two. And then Question 6, which mentions that the Holy Father gave one reason for the popularity of the Mass as nostalgic longing but conveniently forgets to mention his OTHER point that young people were being increasingly attracted to it as well. So as usual, some American Bishops can't avoid putting their own spin on things.
However, in the dross I found this question (and answer) intriguing, because I didn't read anything about this in the document itself:
Question 17:How does the new Apostolic Letter differ from these previous provisions?
The Apostolic Letter of Pope Benedict XVI differs from the previous provisions in the following ways:
What books may be used?
(under Quattuor Abhinc Annos and Ecclesia Dei Adflicta) The 1962 Missale Romanum
(under Summorum Pontificum) The 1962 Missale Romanum and all other Roman liturgical rites in force in 1962
This, if true, is very promising.
UPDATE: People who know these things on other blogs say "rites" here means the other sacraments, not different rites of Mass. They are probably right...definitely be interesting to see what this means for the other liturgical uses though! I find it hard to believe that the Pope has it in mind to exclude them.