You've touched on a fundamental issue, Sean.
There are limits to what can be done with the "we provide the sacraments, you avail yourself of them IF YOU WANT TO", or "Laity/each man's conscience in the drivers seat" strategy that has been the bulwark of the Traditional Movement.
When it comes to Mass and the Sacraments, it works. Each person has his own opinion, his own lights, and he goes to Mass where he thinks best. If he doesn't like Mass at one location, he can go to another.
But there are limits to what can be done in the absence of an absolute, unquestioned authority (Rome). Supplied jurisdiction falls short on things like Marriage Tribunals.
Why? Because human nature. That's why. People don't like to be alone. They don't like living in bad marriages. People want to be loved. It's normal and natural. And even the most objective of human beings (the 1%) aren't fully objective when it comes to their own case. So it's a real problem.
Let's just say there's a moral hazard in play here. Couples would be inclined to go -- not chapel shopping, but MARRIAGE DECISION shopping -- going from group to group until they get the decision they "feel is right" -- the one they wanted in the first place.
How does one replace THE PAPACY or MARRIAGE TRIBUNALS? Short answer is, you can't. Marriage Tribunals by their very nature are AUTHORITATIVE, UNIQUE, and FINAL. You can't get that with the current "Traddieland" milieu.
Some can TRY -- replace the Pope with the SSPX Superior General, and Ecclesiastical Marriage Tribunals with SSPX tribunals where you make a private vow swearing to abide by the decision. It's clunky, but it's the best they can do. It's way clunkier than setting up Mass centers and offering the Mass. That's pretty straightforward by comparison.
Yes, this is the $1,000,000 question: What are the limits and extent of supplied jurisdiction amidst a state of universal grave spiritual necessity?
That question will be answered differently, depending on the faction:
Resistance and old-SSPX, who generally take a more
theological view of the crisis and its remedies will take a more expansive view of its extent/limits, and say that because salvation of souls is the highest law, and because jurisdiction is made for souls (and not souls for jurisdiction), that jurisdiction extends to every aspect of the apostolate necessary to extricate souls from said necessity.
The viewpoint would be corroborated by +de Mallerais' 1991 study
Supplied Jurisdiction and Traditional Priests:
http://archives.sspx.org/miscellaneous/supplied_jurisdiction/supplied_jurisdiction.htm Sedevacantists, who generally take a more
canonical view of the crisis and its available remedies will take a more restrictive view of the extend and limits of supplied jurisdiction (an observation corroborated by sedevacantists general disagreement with +de Mallerais).
Indulters (who contradictorily admit the existence of a crisis in the Church, yet deny it amounts to grave general spiritual necessity) will naturally take an even more restrictive
legalistic view, saying supplied jurisdiction cannot come into play at all (except in the narrowly defined instances enumerated in the 1983 Code).
After a bit of reflection, my unqualified opinion is that the SSPX probably believes its tribunals fully authorized by supplied jurisdiction (given its acceptance of +de Mallerais' thesis), but replaced authoritative annulment decisions with vows of the faithful for pastoral reasons (knowing some faithful would question supplied jurisdiction vis-a-vis annulments).
Hate to say it, but the more I consider the matter, the more I believe +de Mallerais was right, because if he wasn't, there'd be countless instances where the apostolate would be paralyzed to the detriment of the faithful (i.e., there would be no means of removing individual souls from necessity).
And of course, restrictive canonical considerations amidst a state of grave general spiritual necessity are presumed dispensed (e.g., St. Thomas Aquinas says that necessity carries within itself its own dispensation; it need not come from the superior).
I'm prepared to be wrong, but its what I think I think.