I also think there is another piece to the puzzle. I think the Church already knows that it is going to buckle in the future on the issue of same-sex marriage, and wants to put up a dog and pony show of faithfulness before the inevitable surrender.
When the Church was facing legislative pressure to drop polygamy, they dug in their heels harder. This was partially a strategic effort to convince Congress that polygamy was an "essential" part of the practice of the Mormon religion, and therefore protected under the First Amendment. If Congress could be convinced that polygamy was essential to Mormonism, then the First Amendment would protect the LDS Church and Congress would let Mormons continue the practice unabated. The more heated the friction between Mormons and American government got, the harder the pro-polygamous rhetoric got.
But the Church lost the standoff and President Woodruff ended polygamy (wink wink). When the Church felt they couldn't fight the government anymore, they just happened to get a "revelation" telling them to drop polygamy so they could be friends with America. This PR document known as Official Declaration 1 was called a "revelation" by early Mormons in a rather tongue-in-cheek manner, as they secretly disregarded it and continued polygamy for over a decade after the fact. If they believed it was a real revelation, they would have stopped immediately in 1890, not later in 1904 when new political pressure required it.
Similarly, as the civil rights movement was in full-swing in America in the '60s and '70s, the Church held to its rhetoric that blacks could not hold the priesthood, even those who had a single drop of African blood in them. As distaste for this position grew both outside the Church and within, the leadership sought Divine direction as to how to handle the matter. When Heaven didn't respond to President McKay, President Kimball continued the appeal. When Heaven didn't respond to President Kimball, he changed tactics. He instead joined with the other leaders (well, a majority of them) and they determined that they were going to go ahead and flip to allowing the ordination of black men to the priesthood, and if God had anything to say against this change, He would be free to do so. As Heaven maintained its silence, the brethren took that as an affirmative silence, a "revelation," and made the change under this purported Divine approval.
I anticipate a similar unfolding in regards to same-sex marriage. The Church is officially digging in its heels against same-sex marriage being accepted within the Church, putting on a big show so the world will know they stood faithfully against gay marriage for so long as God required it of them.
Then, when the legal opposition gets too tough and the membership makes a majority shift to supporting same-sex marriage within the Church (which is a growing trend), the brethren will determine to shift position and allow same-sex marriages to be recognized and performed within the Church, even within temples. They will grant God an opportunity to cast an opposing vote, and in His silence they will infer approval and claim a "revelation" from God switching the Church's stance.
But having learned from prior events, they have been laying groundwork in the interim that they will then be able to point back at to say "Look, God was laying the groundwork for this for a long time beforehand, preparing the way." And the membership will eat it up. The leaders will point to the Church's support webpages for gays, the Church's endorsement of legislation protecting people on grounds of homosexuality, the Church's monetary contributions to gay organizations, the Church's allowance of members to support same-sex marriage (except their parent's), and other such calculated efforts made by the Church to appease the discontent masses.
The groundwork will have been laid, a silent "revelation" will be referenced with no content of said "revelation" ever being quoted, and same-sex marriage will become a part of the LDS Church. They will be able to claim that they were faithful in God's restriction to heterosexual marriages until the end, because of dog and pony shows like this policy change, and then they will be able to claim faithfulness to the unchanging God's newly changed mind as they embrace His purported shift of position within the Church. That is my theory of how this policy change fits into the bigger picture.