So does the Moto Proprio do anything new? Not really. There are already priests who have permission to celebrate mass according to the 1962 Missal, some do so in private, some do so in public. There are some parishes that do everything according to the 1962 Missal (including the Good Friday prayers), in particular those administered by the Fraternity of St. Peter.
Will we see vast hordes of priests start to celebrate the 1962 Mass in private? I don’t think so. They aren’t even celebrating the current mass in Latin, in private or in public. Will people stream to those churches offering it? I don’t think so. Houston has had it at 8:00 a.m. on Sunday at Annunciation for years, and people aren’t flocking to it (the crowds are going to Minute Maid Park next door).
All it does, it seems to me, is let the priest make some decisions on his own without having to beg permission of the bishop.