Thanks for the clarifications.
It is not 100% reliable to base predictions on these private PCED letters. However, I think decision could signal that any Roman deal with the Society will not necessarily include "friends of the Society." I'm thinking the affiliated independent Chapels will need to somehow formally become part of the regularized Society or else make peace with their local Bishop for the Society to affiliate with them. I think from Rome's perspective they have to do this so that all the priests they regularize are "under them" in some sort of way. Rome can't have "free agent" priests out there who are regularized but accountable to nobody. This might create a problem as many Traditional independent priests who have been working with the Society may not want to give up their freedom to formally join them. Then again, the Society could make a provision for them, allowing them to function as is and stay put. Nevertheless, these formally independent priests would, in the end, need to take orders from Bishop Fellay and the District Superior.
If regularization happens I see the majority of the Society going with Bishop Fellay with a minority contingent sticking with independent priests and those priests who leave or who are kicked out of the Society for opposing regularization. The problem is, unless all of these priests unite together under one Bishop or leader, they may very well suffer the same fate as the Sede communities and turn into isolated pockets of faithful, eternally splitting and arguing amongst each other. The Society's practical strength was and is its hierarchical organization, seminaries, etc. It was founded well by ABL who had experience with the Holy Ghost Fathers in formation and setting the statutes and running an order, building schools, priories, etc.
As far as the Sunday obligation is concerned, I'm not sure how Msgr. Pozzo's decision in this case squares with the Canon Law, as Fr. Roberts said on Rorate. The new Canon is very broad. Mass in a Catholic Rite is all that is required. He also points out that in certain circumstances, an Orthodox Mass even fulfills the Sunday obligation under the New Code. At least one objector on Rorate says that "Catholic Rite" may mean a Mass said by a licit priest. But, to me, that makes no sense. The Code refers to the Rite, not who says the Rite. I think we can assume the Code means it to be said by a valid Catholic priest, or else it would be silly. But can we say this canon assumes liciety also? Especially when previous guidance from the PCED seems to have said that Society Masses do fulfill the Sunday obligation? And in this case, Fr. Robert's canonical situation is even more certain than the Society's if he has not been suspended. From what he posted on Rorate it sounds like he is in limbo of sorts.
The problem is if we interpret "Catholic Rite" broadly, this would mean that assisting at an Old Catholic Mass or a liberal Novus Ordo said by a suspended liberal priest would fulfill the Sunday obligation as well, which would seem ridiculous. Yet both the priests in that scenario, Rome would see as valid priests and the Masses as valid Masses said in a Catholic Rite. Then we are back to the liceity of the Mass, but the Society's Masses are not "licit" in the eyes of Rome, yet I believe the PCED prieviously stated they fulfilled one's Sunday obligation.
In the end, complete confusion as far as I can see. Does anyone know what the old 1917 Code had to say on this subject? Thanks.