Same-sex marriage will be codified by the Church within a few years, along with much more depravity.
Some collection of bishops might try but the Church will not. Any bishops, including the pope, who would attempt to sanction same-sex marriage would be guilty of heresy and would place themselves outside of the Church. The true church would not be those who hold title to the deeds of the church building but those bishops and the faithful who hold on to the teachings of Scripture and Sacred Tradition.
In the Catholic Church there are clear lines that cannot be crossed. That is why the liberals hide their agenda in ambiguity and disingenuous calls for "dialogue." If they were to clearly show their hands and unambiguously reject church teaching they would place themselves outside of the Church.