I hope it is, the last thing we need is for this epic Decade movie to be one of those good-for-nothing "Alternate Ending" movies like Blade's & Ryuki's movies were. That'd be an utter disappointment
I don't want to see the movie out of continuity, but I don't want it to be the ending either. Narutaki there still was a mysterious figure there and Decade's amnesia apparently wasn't explained either.
If this last world is post-movie, they'll be able to explain those details and Decade's original mission given by Wataru. Besides, doesn't the preview say that the real enemy isn't Daishocker? It'll be weird if they defeat the "real" enemy before the "fake" enemy.