Let's talk about a hypothetical.
Say Fr. Pfeiffer became sedevacantist (or, some might say, "embraced his inner sedevacantism"). And being a man of action, he embraced Conclavism. He called for another one of his priest meetings, inviting all the priests that will still talk to him, and gets ? of them to meet in Boston, KY or elsewhere to elect a Pope. (The exact number isn't important, so I will pass on that point)
Obviously, himself being the de-facto leader and alpha male, most (or all) of the priests vote for Fr. Pfeiffer, who takes the name Pope Joseph I.
What would he do in the coming weeks?
1. He would wear a white cassock.
2. He would also wear a white skullcap (or Papal crown, if he could get one).
3. He would be isolated from other Catholic communities, treating his group as if they were the whole Church.
4. Building on #3, he would insist that his followers red-light other "Trad" groups, including the SSPX, sedevacantists, indult, or even Resistance priests not in union with Boston, KY
5. He would take a commanding role in the Traditional movement against Vatican II, insisting that all priests and bishops follow his leadership.
6. He would bind and loose, controlling his followers and dispensing them from Sunday Mass attendance if they aren't physically able to attend Mass at a chapel in union with Boston, KY.
7. He would tell his "faithful" that the Church commandment "Contribute to the support of the Church" is only met by donating to the TRUE Church, which is centered in Boston, KY with himself as Pontiff.
8. He would attack all other so-called Traditional Catholics as infidels, since they are at the very least schismatic, not recognizing his Papacy and authority.
9. Building on #8, he would probably focus MOST of his attacks in this direction (against other Trads), since it's easiest to make converts from among existing Traditional Catholics, compared to Novus Ordo Catholics, protestants, or atheists.
10. He would insist on running a seminary, since the Catholic Church needs at least one seminary, and there certainly aren't any others in the world! After all, only CATHOLIC seminaries count, and being in union with the Holy Father is a requirement for being Catholic. All other Trads are at least schismatic, since they don't acknowledge his papacy.
11. He would not go easy on those who don't acknowledge his papacy, especially priests and bishops. He would treat them with a heavy hand, as malicious schismatics and enemies of God. He would preach against them often.
12. He would have a bunker/remnant mentality, and would encourage such an attitude in all his "faithful". He would fly around the country, and even around the world, rallying the troops and encouraging them to "keep the faith".
13. Building on #12, he would be the center of unity for his "faithful". It wouldn't be a cult of personality, because he is the Pope, and the Pope is the principle of unity in the Catholic Church.
14. He would pontificate as one with authority, and one with a special destiny from God.
15. When anyone (layman, priest, or even bishop) disagreed with him on any point of morality or theology, Fr. Pfeiffer would denounce him as being in-the-wrong and heretical, and probably malicious as well.
16. He would think nothing of setting up small "missions" everywhere, even in cities that already have a thriving Resistance chapel, albeit a chapel not in union with Boston, KY. So it's not Catholic, of course, but schismatic! What good is it?
Obviously you see my point. Except for #2, these things are all happening today, May 3rd, 2016!
Just like we say, "Who cares if the SSPX deal with Rome has been consummated or not. They've already changed, they've already given away the farm!" The same with Fr. Pfeiffer. Who cares if he ACTUALLY CALLS A CONCLAVE, gets elected and takes a Papal name, and puts on the white skullcap. He's doing everything else today!
The SSPX singing a formal deal, or Fr. Pfeiffer getting elected, is just a formality. The consequences of such a "formality" are already with us as a reality, so who cares if the formality never comes, at this rate?
It's like they say, "with friends like this, who needs enemies".
In this case, it's "With non-claimants to the Papacy that act like this, who needs minor antiPopes?" or "With not-officially-approved-by-rome-organizations that compromise like the SSPX has, who needs an actual contract or dotted line signature"?