It is a common enough opinion that the social reign of Jesus Christ, proclaimed so clearly by Pius XI in Quas Primas and commemorated every year in the Feast of Christ the King, was abandoned or rejected by the Second Vatican Council.
And he goes on to attempt to show that this is not so.
Liberals (and traditionalists) may at this point reasonably object: "If the Second Vatican Council and John XXIII clearly believed and preached the social reign of Jesus Christ, why is it no longer reaffirmed in teaching? Why did everyone after the council act as if Quas Primas had never been written?" Certainly, many things that were proclaimed and enacted during the council were discarded afterward. Pope John XXIII, to use one example, was spared the indignity of seeing his apostolic constitution On the Use of Latin (Veterum Sapientiae), promulgated during the council in the assembly of bishops and cardinals, vanish from public knowledge immediately after the council; many collections of Pope John's writings do not include it, and most biographies do not mention it.
While Quas Primas is on the Vatican web site in English, Veterum Sapientiae appears to only be available there in Italian. I did find it in English at the Vancouver Traditional Mass Society. [Or, if no longer there, at Adoremus. --ed.] Pope John concludes
With the foregoing considerations in mind, to which We have given careful thought, We now, in the full consciousness of Our office and in virtue of Our authority, decree and command the following: ...
Followed by a series of instructions to bishops and others on the use of Latin which, believe it or not, do not appear to have been followed since.
I don't know that the Church could retrace its steps and implement Pope John's instructions, but it might be a place to begin retracing steps in a failure analysis of the Second Vatican Council.