We still have next month for the scans to reveal the two final worlds, which could be Olympus Coliseum and another one possibly Atlantica. And that part of the scene where Ven and MX met could just be a concept included for the trailer only, possibly Nomura and his team might be in a process of developing new areas of the world of Olympus Coliseum (possibly Mt Olympus and the City of Thebes), that's why he included that scene with the Coliseum area in it (which could be taken out of the game) but that doesn't mean the world is taken out.
Kinda like Terra and Ven scene in Radiant Garden, where the cliffs is the same as KH2 but now the scan of the world is reveal, the cliff from KH2 was not shown on the artwork.
And of course, it would be cool to see young Herc training to become a hero under Phil back then when he was a teen.