We don't need a "universal indult" - just an admission that "Quo Primum" is still in force i.e. that the traditional Latin Mass has never been abrogated (and that all priests of the Roman rite are "always and everywhere" free to offer this form of the Holy Sacrifice).
Of course, it would help if the pope issued a humble apology to all those priests who were "excommunicated" for abiding by their oath against modernism and courageously persisting with the Holy Mass of their ordination.
Unfortunately, the only papal apologies these days are to schismatic orthodox sects, lutherans, jews, mohammedans etc etc. -
And for what does our holy father apologize?
Zealous attempts at evangelization - now called "sins of the past".
If that were the case, Priests that chose to celebrate the Tridentine Mass, would still be under the influence of the local Bishop (which I would say there is no way around in any case) and those Bishops could still refuse to allow it, (after all the Churches still 'belong' to them) and if they allowed it, could/would force concelebration and all that implies.
It will all come about someday that we don'thave to scheme against the Church in order to have the Mass of the ages.
Despite what my little pea brain thinks what is best for the Church, I defer to the Holy Trinity, and I ask everybody here to join together in prayer for His Will to be done. I know you all do, so I join my prayers to yours.