The ONLY possibility of a universal indult would be IF the SSPX officially accepted VATII teachings, or something very close to it.
In that case it would be “IF you accept VATII, we’ll issue a U-Indult.” kind of thing.
The U-indult persuasion is a biggy primarily for the SSPX.
However, the whole reason for SSPX is just as much rejection of VATII as it is the Traditional Mass.
I do not see the SSPX accepting VATII for another generation if then, so the U-indult is no more likely.
Think about it; what would the pope gain for such a horrific tumult in the church?
So, no U-indult even on the horizon to be realistic.
That’s not to say that he will not reign in the “flex masses” of the NO and promote more Latin useage in that mass as well as Gregorian Latin music. That is, dress up the NO to appear more connected to Traditional masses.
But U-indult…forget it. Such a thing depends too much on the SSPX capitulation.