My understanding is that priests and laypeople in those regions where the Ambrosian Rite has historically been used have encountered great resistance from authorities who should be supporting their interest in the older form of the Ambrosian Rite, with the 1954 Missale Ambrosianum, as it was before it was reformed (the parallel of the 1962 Missale Romanum).
A priest friend of mine, Fr. Jeffry Moore, serving in the Diocese of Lugano is stationed at Ascona. He has gotten involved in the matter and has obtained some results. As a priest of the Diocese Lugano, he belongs to a bi-ritual clergy. There are many places in the area where the parishes are distinguished as Ambrosian or Roman. Fr. Moore’s church has the distinction being of both rites. Altars are designated specifically for the Ambrosian Rite. His church in the past actually had a different sacristy for the Ambrosian use.
People in the region are very sensitive about their Ambrosian identity.
Fr. Moore wrote to the Pontifical Commission Ecclesia Dei on 7 January 2009, which was hand delivered, and followed up with a meeting with Card. Castrillon Hoyos on 9 January together with 2 priests from Milan and 2 lay people.
At that time Fr. Moore was told that Summorum Pontificum applies also to the Ambrosian Rite.
Fr. Moore has now received a letter from the Secretary of the Commission , Msgr. Perl, as a follow up.
Fr. Moore asked me to put this up for all to see.
Here is (the author of the original letter to the PCED) Fr. Moore’s translation of that letter from the Italian original:
Your letter of January 7, 2009 has had our attention but is still waiting for a reply. You express a desire to “receive the comfort of having the approval of the possibility that also your Ambrosian students who ask for it can enjoy the benefits guaranteed by the Holy Father” in the Motu proprio “Summorum Pontificum”.
While it is true that the Motu proprio of the Holy Father does not expressly cite the Ambrosian rite, it doesn’t exclude the other Latin rites; if the will of the Holy Father asserts for the Roman rite, considering that it is superior in dignity, consequently much more for the other Latin rites, including the Ambrosian rite.
Wishing the blessings of the Lord on your pedagogical work, I greet you fraternally.
This is important not just because it applies to the Ambrosian Rite, but also for all the other Latin Rites which under law were in use before the reforms. This would include the Dominican Rite, in which many religious have interest.