Since they started making deals with the modernists and kicking Bishop Williamson out, I have always remarked on what a cult they were.
At home with neither the modernists they were trying to "convert", nor the resistance which was actually fighting for the faith, they could only turn inwards. And it is which made them a cult.
Everything was about them, about their Masses. Outside the SSPX no salvation.
Now with the excommunication they have finally got a punishment for this self delusion, and I could see them go the way of the St. Benedict center. Out on their own.
But Rome probably wants to toy with them more. Whatever take the attention away from the Resistance and its Bishops.