The misreading of "continenter" needs to be kicked firmly into touch. The Holy Father speaks of young people who have discovered this liturgical form and felt its attraction etc. He also says that the norms are
"meant to free Bishops from constantly having to evaluate anew how they are to respond to various situations"It cannot be in accord with the mind of the legislator to say that people cannot now ask for the older form of the Mass if they have not asked for it before. That is not what "continenter" means in the context. It is not a strengthening of "stabiliter" which has a precise canonical meaning, but a weakening of it, probably to prevent a restrictive interpretation. A group that exists "continenter" is a group that has not just been gathered together "ad hoc" for a particular occasion.
The questions that are asked can reveal the mindset from which they come. To ask
1. Why has the Pope seemingly taken a step backwards in allowing the former Tridentine rite of Mass alongside the one we have now?and
3. What form of Mass is allowed by the Motu Proprio?give the impression that this is another indult, a permission of something generally forbidden. That was how most post-conciliar liturgists always used to think: this is the mindset that now needs to change. Article 1 of Summorum Pontificum sets out the fundamental principle of the document. It is a principle denied by establishment liturgists for decades and now quite clearly affirmed by Pope Benedict: it is permissible to use the 1962 missal because it was never abrogated.
Hence no priest needs any permission to celebrate this form of the Mass privately. It is not a question of when this form of Mass might be allowed but when, for particular reasons, it is not allowed. In a normal parish, it is not allowed to change all the Masses to the older form: it is specified that on days of precept, one may be said. (Presumably the Ordinary could dispense from this restriction for any reasonable cause.)
Apart from this, there may be any number of circumstances in which the priest may use his pastoral judgement in choosing to use the older forms of the rites. The Motu Proprio says (5.3) that the extraordinary form should be allowed by the Pastor for faithful or priests who request it, "such as marriages, funerals or occasional celebrations, e.g. pilgrimages." Note the "e.g."
It is worth learning the following part of Pope Benedict's accompanying letter by heart to quote when talking to liturgists who argue according to the mindset of an era that has now been drawn to a close by Summorum Pontificum:
In the history of the liturgy there is growth and progress, but no rupture. What earlier generations held as sacred, remains sacred and great for us too, and it cannot be all of a sudden entirely forbidden or even considered harmful.By way of a footnote here, may I gently suggest, biretta on head, that it is best to stick to the issues rather than making personal comments about an individual. As Mr Meagi would say, "Focus!"