Originally Posted by
Sacred Knight
Basically at this point the two most likely ideas are that the two Supermen are the still-split Superman Red/Blue incarnations. The idea being that it'll be retconned to reveal they never actually remerged by that story's end. Or, they're the same man from different time periods due to various time space continuum shenanigans. Both ideas perpetuate though that both incarnations are "real" and that they will fuse back together into one when things are set straight.
But these two theories have a leg up on virtually any other at this stage of the game.