The story broke not long ago about some new clarifications on Summorum Pontificum from the Pontifical Council Ecclesia Dei. I got it from the New Liturgical Movement folks, and I thank them for helping to get this story out. Here are the clarifying items, as summarized by the NLM guys:
1. If there is no other possibility, because for instance in all churches of a diocese the liturgies of the Sacred Triduum are already being celebrated in the Ordinary Form, the liturgies of the Sacred Triduum may, in the same church in which they are already celebrated in the Ordinary Form, be additionally celebrated in the Extraordinary Form, if the local ordinary allows.
2. A Mass in the usus antiquior may replace a regularly scheduled Mass in the Ordinary Form. The question contextualizes that in many churches Sunday Masses are more or less scheduled continually, leaving free only very incovenient mid afternoon slots, but this is merely context, the question posed being general. The answer leaves the matter to the prudent judgement of the parish priest, and emphasises the right of a stable group to assist at Mass in the Extraordinary Form.
3. A parish priest may schedule a public Mass in the Extraordinary Form on his own accord (i.e. without the request of a group of faithful) for the benefit of the faithful including those unfamiliar with the usus antiquior. The response of the Commission here is identical to no. 2.
4. The calendar, readings or prefaces of the 1970 Missale Romanum may not be substituted for those of the 1962 Missale Romanum in Masses in the Extraordinary Form.
5. While the liturgical readings (Epistle and Gospel) themselves have to be read by the priest (or deacon/subdeacon) as foreseen by the rubrics, a translation to the vernacular may afterwards be read also by a layman.