Your posts do intrigue me though because you don't seem to fall into either camp (SV or non-SV) and I'm still left wondering where you stand. If I'm accurate in stating this, exactly how do you explain the crisis? Is there some other option I'm not considering?
I would call myself tongue-in-cheek a "sede-doubtist". I personally believe that it's extremely likely, almost virtually certain, that the Holy See is vacant. But I also believe that the Church must make definitive judgment on the matter and that I cannot usurp the authority of the Church in that regard. I believe that Cardinal Siri was most likely elected in 1958 and that the subsequent elections through 1989 (the death of Siri) were invalid. Then you have Benedict XVI who most likely did not possess valid episcopal consecration, and Francis I, who may not even have valid priestly ordination.
Legitimacy of a pope is a dogmatic fact and must therefore be known
a priori with the certainty of faith.
Here's my illustration of the problem. Let's say I'm living at the time of Pius IX and believe that the dogma of infallibility is heretical. All I would have to say is that Pius IX was a heretic in order to reject the dogma of infallibility.
If anything, I find the Cassiacuм theory appealing (formal-material pope distinction); it makes the most sense to me.
I'm not convinced of the St. Robert Bellarmine position regarding heretical popes, but I personally consider it objectively heretical to say that a legitimate Pope could promulgate a harmful rite of Mass and that an Ecuмenical Council certified by a legitimate Pope could teach grave error to the Church.
And THAT is my biggest problem with Traditional sedeplenism; I would have been universally condemned as a heretic 75 years ago if I held that the Church could do this.