Matthew wrote: "...In other words, they shouldn't be called Sedevacantists but something more inclusive. They aren't rejecting just the pope, but about 1 billion Catholics as well..."
I don't understand what you're saying in your post, but as to what I quote above, I was thinking about some things.
I don't think anyone should be declared as absolutely outside the Church unless one of two things are true:
1) The individual himself declares that he is not Catholic; or
2) The individual's personal doctrines are heretical even though he, himself, knows what the doctrines of the Catholic Church are.
It is very possible that many of these 1 billion self-professed Catholics are indeed Catholics because they have been so poorly educated about the faith that they truly believe the heretical doctrines they hold are authentic Catholic doctrines but would, if corrected, submit to the true Faith of the Catholic Church. In many instances, this docilitiy can only be known by God. In many Western countries, however, the vast majority of self-professed Catholics know that they profess heresy (as many polls indicate) and will admit, "I know what the Church teaches, but..." These individuals should never be considered to be Catholics.
In the case of the clergy, however, I cannot accept that but only a very, very few do not know what the Church teaches on most matters of doctrine and I certainly cannot accept that one who headed the Congregation of the Doctrine of the Faith for years is ignorant of the True Faith, even though he may really think that Truth can change over time as is what most Modernist priest and bishops today believe. (Remember that as Father Ratzinger, Benedict XVI did take the Oath Against Modernism--He positively knows that the Church teaches that Truth [i.e., doctrine] does not change.)
I wonder when, precisely, a faithful Catholic in England realized that the Church he had been baptized in and attended every Sunday and Holy Day was no longer Catholic or when the average citizen of England was no longer Catholic and when the average citizen no longer even considered himself Catholic. We seem today to be in that transition period in the Church, though I hope and I pray that the Crisis will one day end and we will have a Catholic pope again.