The three-year term simply refers to a balance of the first three years of application. If there turn out to be serious difficulties, appropriate remedies will be found, always keeping in mind the essential purpose of the motu proprio.
Interview with Msg Guido Pozzo, Secretary of PCED
Looks like Pope Francis may be getting ready to pull the plug on Pope Benedict's Summorum Pontificum.
Pozzo, in that same position, also said:
I am convinced that the questions which hinder the full reconciliation of the SSPX with the Holy See have to do with doctrine. Full text of Msgr. Pozzo Interview
I wonder what "doctrine" Msgr Pozzo was referring to?