How can any authority be enforced without a real Pope?
The SSPX leadership knows this, and has developed a kind of cult of (blind) obedience after Abp. Lefebvre passed away. There has to be some fear or threat, otherwise, there is no good reason to follow this or that authority, since everyone knows that it is not a real, but merely a make believe authority. This is how the SSPX does not fall apart like the Resistance does.
In the end, it seems that people will naturally follow this or that bishop, simply because he has the powers that the priests don't, and people need him for the sacraments. So, the bishops naturally will have an authority because they are more powerful. Nothing apart from this will work, in my opinion.