The rumors, apparently, are that this "alternate world" is the Pre-Crisis Earth 2, or a version of it where the Crisis never happened (and it's still the 80s).
I am beginning to believe, DC created a new multiverse from pieces of the old with some additions. While "Earth-2" was spoiled back in Justice League of America #0, the Wildstorm Universe was definitely added via Ion and Uncle Sam and the Freedom Fighters perhaps is another New Earth. USatFF #8 discusses Shadow Demons and what is to come, probably another big event. I am unsure if this series is set in the current DCU. Of course, I am not sure any series is set in one universe or continuity. For all we know, Superman and Action Comics take place on different earths.