If this actually happens (and I have my doubts), then it is just a policy change as evidenced by the fact that civil marriage first is the SOP in other countries. If the one year penalty for marrying civilly prior to the temple was a doctrine, then they would enforce it in all countries where they have a presence.
Yes it should be a "revelation" and not a policy change. Governments and bureaucrats have policy changes; the supposed "one true church" should expect nothing less than a revelation. And if they're having trouble coming up with how to write the revelation, I'm sure the good folks here would be more than happy to assist.
Besides, a revelation would cause TBMs to have a renewed faith in continuing revelation and silence the critics about no new revelations since... 1890.
So what what this marriage change rumor anyway? It seems to be intentional misinformation or was it a trial balloon by their leaders?
It is not a command from God. My wife and I were able to marry back in '68 in our home ward and then five days later we were sealed in the temple. We had permission from the First Presidency and carried a letter to the temple president to that effect.