Mention has already been made about the similarity between past comments made by some Branch-Theory Anglicans who wanted reunion with Rome on their terms at the time Anglicanorum Coetibus was released, and SSPX Bishop Williamson's comment, that suggests that the Catechism of the Catholic Church is somehow other than the entire body of Catholic dogma and morals. Williamson wrote,
The rumour from Rome is precisely that he is thinking of a "Motu Proprio" which would accept the SSPX "back into the Church" once and for all, yet require from the SSPX no explicit acceptance of Vatican II or the New Mass, but only, for instance, the acceptance of John-Paul II's 1992 "Catechism of the Catholic Church", which is substantially modernist but in a quiet way.
But another similarity occurred to me that also ocurred to another commenter:
For the longest time it has been predicted that Bishop Williamson would not go along with any agreement made by Bishop Fellay with Rome, so this is not new news. The rumor of the MP is new, of course, and maybe it will come to pass, who knows? If +Williamson splits off from the SSPX over the deal, that would only follow the pattern of other groups in somewhat similar situations. When the Russian Orthodox Church Outside of Russia (ROCOR) was in process of reconciling with the Moscow Patriarchate, a similar split of a small group, under some bishop who has since sunk into anonymity, occurred. That did not stop the reconciliation, of course.