[charliemarlow]

Since one pope cannot bind another, even in the strongest terms imaginable, then we can look forward to a full correction of the items in Tantumergo's e-mail.
But, wait, no one anywhere ever said Quo Primum was nullified! It's still in effect!

[gbcdoj]

But, wait, no one anywhere ever said Quo Primum was nullified!

Yes, they did.

... from the day on which the translated texts must be used for celebrations in the vernacular, only the revised form of the Mass and [the breviary] will be allowed, even for those who continue to use Latin. (Instructione de Constitutione, AAS 63 (1971) 712–715.)

[BlackElk]

Quo primum was, in legal terms, ultra vires or beyond the powers of even a pope insofar as Pope St. Pius V purported to excommunicate in advance anyone who dared tamper in any way with his missal. This sort of thing falls into the realm of prudential judgment and not dogma. He also did not have the power to excommunicate a successor pope for wearing what he might have deemed the wrong kind of shoes or for signing in a cvolior of ink not pleasing to Pius V.

John Paul II need not lose sleep worrying about any future pope overturning the excommunications of Marcel or the decree of schism against SSPX. The SSPX may evaporate or its adherents may recant and repent and do penance for their crimes and those of their excommunicated leaders and schismatic forebears, as the case may be, in which event, the Catholic Church will, no doubt, consider their re-admission.

SSPX. Something about a flea, an elephant's leg and a yearning for an indecent act.