Over at WWE.com, a poll is currently running (on the front page, as of this writing) with a result that shouldn’t be shocking in the slightest:
There are reports that say WWE has already decided this match will indeed be the main event. That said, Seth Rollins and Paul Heyman have been throwing that designation around in promos building to Rollins challenging Brock Lesnar for the Universal title on the very same show. Perhaps WWE will attempt to market a “double main event” or something to that effect, which is really just a promotional trick that doesn’t mean anything. The main event is the match that goes on last.
If they really want to give the fans what they want as the McMahon family claimed on television not so long ago, they’ll put Rousey vs. Lynch in that spot.